摘要:

OF MILK: CORRECTION FACTORS AND THE INFLUENCE OF STIRRING: I1 h I11 225 It was originally intended to employ four different amounts of supercooling for each sample of milk, vix. about 1.5, 1.0,0.8, and 0.5" C. It was found, however, that the differences in the readings of the thermometer corresponding to these different amounts of supercooling were in the neighbourhood of 0.002"-an amount so small that the unavoidable errors of observation might possibly approach the same order. It was, therefore, decided to employ only two different amounts of supercooling, as widely apart as practicable, say about 1.5" and 04", and to increase the number of samples examined. It was stated by Hortvet that, unless a much greater amount of supercooling than 0.5" is employed in the use of his cryoscope and technique, the rise of the mercury column is not sufficiently pronounced, and that there is more or less wavering, so that difficulty arises in deciding on the exact point at which the top of the column becomes stationary. Elsdon and Stubbs (Eoc.it.)^ found the same result when using a supercooling of less than about 0.8"; the mercury rose very slowly, and did not maintain a steady position for any appreciable time, and the proper freezing-point might not, under these circumstances, be attained. In the first experiments, made with the object of ascertaining the super- cooling correction, it was observed that where the amount of supercooling was small, that is, less than say 0-75", even in the absence of alcohol in the jacket surrounding the freezing-tube, the rise of temperature, when freezing occurred, was very slow-so slow, indeed, as to suggest doubts whether the thermometer would indicate the freezing-point of the milk, influenced only by supercooling, owing to the reading being affected by the length of time which elapses and the possibility of imperfect thermal insulation, causing a nett loss of heat from the freezing tube and contents.To give an instance; in an experiment when the supercooling was 0-71" the time required for the mercury column to rise until, on observation through the telescope with the aid of the horizontal cross-wire, the ascent became imperceptible, was 92 minutes, as compared with about 3& minutes when the same milk was super- cooled 1-49'. It will be seen later that, in the absence of alcohol in the space surrounding the freezing-tube, the heat insulation of the milk is not perfect; a nett loss of heat occurs, for it is possible t o carry through a freezing-point determination under such conditions.The difference between the two methods of working- with and without alcohol-results in a longer time being required for the cooling of the milk when the space around the freezing-tube is occupied by air. There were also the difficulties of judging when the rising column of mercury had reached the highest point, due to the very slow movement which occurred in that region, and of getting satisfactory readings, owing to the short time that elapsed before a fall took place. The idea of following strictly the Hortvet technique, as regards stirring, for these particular experiments was therefore abandoned.In the first series of experiments, the results of which are recorded in Table 111, four or five stirrings of three strokes each were employed, and in the second series the mechanical stirrer, working at the rate of 40 strokes per minute, was in operation all the time, the thermometer rising until tapping became necessary. It does not appear that these variations in stirring caused any significant differences in the results obtained, but the times of rising of the mercury, after two different extents, large and small,OF MILK: CORRECTION FACTORS AND THE INFLUENCE OF STIRRING: I1 h I11 225 It was originally intended to employ four different amounts of supercooling for each sample of milk, vix.about 1.5, 1.0,0.8, and 0.5" C. It was found, however, that the differences in the readings of the thermometer corresponding to these different amounts of supercooling were in the neighbourhood of 0.002"-an amount so small that the unavoidable errors of observation might possibly approach the same order. It was, therefore, decided to employ only two different amounts of supercooling, as widely apart as practicable, say about 1.5" and 04", and to increase the number of samples examined. It was stated by Hortvet that, unless a much greater amount of supercooling than 0.5" is employed in the use of his cryoscope and technique, the rise of the mercury column is not sufficiently pronounced, and that there is more or less wavering, so that difficulty arises in deciding on the exact point at which the top of the column becomes stationary.Elsdon and Stubbs (Eoc. it.)^ found the same result when using a supercooling of less than about 0.8"; the mercury rose very slowly, and did not maintain a steady position for any appreciable time, and the proper freezing-point might not, under these circumstances, be attained. In the first experiments, made with the object of ascertaining the super- cooling correction, it was observed that where the amount of supercooling was small, that is, less than say 0-75", even in the absence of alcohol in the jacket surrounding the freezing-tube, the rise of temperature, when freezing occurred, was very slow-so slow, indeed, as to suggest doubts whether the thermometer would indicate the freezing-point of the milk, influenced only by supercooling, owing to the reading being affected by the length of time which elapses and the possibility of imperfect thermal insulation, causing a nett loss of heat from the freezing tube and contents.To give an instance; in an experiment when the supercooling was 0-71" the time required for the mercury column to rise until, on observation through the telescope with the aid of the horizontal cross-wire, the ascent became imperceptible, was 92 minutes, as compared with about 3& minutes when the same milk was super- cooled 1-49'. It will be seen later that, in the absence of alcohol in the space surrounding the freezing-tube, the heat insulation of the milk is not perfect; a nett loss of heat occurs, for it is possible t o carry through a freezing-point determination under such conditions.The difference between the two methods of working- with and without alcohol-results in a longer time being required for the cooling of the milk when the space around the freezing-tube is occupied by air. There were also the difficulties of judging when the rising column of mercury had reached the highest point, due to the very slow movement which occurred in that region, and of getting satisfactory readings, owing to the short time that elapsed before a fall took place. The idea of following strictly the Hortvet technique, as regards stirring, for these particular experiments was therefore abandoned. In the first series of experiments, the results of which are recorded in Table 111, four or five stirrings of three strokes each were employed, and in the second series the mechanical stirrer, working at the rate of 40 strokes per minute, was in operation all the time, the thermometer rising until tapping became necessary.It does not appear that these variations in stirring caused any significant differences in the results obtained, but the times of rising of the mercury, after two different extents, large and small,OF MILK: CORRECTION FACTORS AND THE INFLUENCE OF STIRRING: I1 h I11 225 It was originally intended to employ four different amounts of supercooling for each sample of milk, vix. about 1.5, 1.0,0.8, and 0.5" C. It was found, however, that the differences in the readings of the thermometer corresponding to these different amounts of supercooling were in the neighbourhood of 0.002"-an amount so small that the unavoidable errors of observation might possibly approach the same order.It was, therefore, decided to employ only two different amounts of supercooling, as widely apart as practicable, say about 1.5" and 04", and to increase the number of samples examined. It was stated by Hortvet that, unless a much greater amount of supercooling than 0.5" is employed in the use of his cryoscope and technique, the rise of the mercury column is not sufficiently pronounced, and that there is more or less wavering, so that difficulty arises in deciding on the exact point at which the top of the column becomes stationary. Elsdon and Stubbs (Eoc. it.)^ found the same result when using a supercooling of less than about 0.8"; the mercury rose very slowly, and did not maintain a steady position for any appreciable time, and the proper freezing-point might not, under these circumstances, be attained.In the first experiments, made with the object of ascertaining the super- cooling correction, it was observed that where the amount of supercooling was small, that is, less than say 0-75", even in the absence of alcohol in the jacket surrounding the freezing-tube, the rise of temperature, when freezing occurred, was very slow-so slow, indeed, as to suggest doubts whether the thermometer would indicate the freezing-point of the milk, influenced only by supercooling, owing to the reading being affected by the length of time which elapses and the possibility of imperfect thermal insulation, causing a nett loss of heat from the freezing tube and contents. To give an instance; in an experiment when the supercooling was 0-71" the time required for the mercury column to rise until, on observation through the telescope with the aid of the horizontal cross-wire, the ascent became imperceptible, was 92 minutes, as compared with about 3& minutes when the same milk was super- cooled 1-49'.It will be seen later that, in the absence of alcohol in the space surrounding the freezing-tube, the heat insulation of the milk is not perfect; a nett loss of heat occurs, for it is possible t o carry through a freezing-point determination under such conditions. The difference between the two methods of working- with and without alcohol-results in a longer time being required for the cooling of the milk when the space around the freezing-tube is occupied by air.There were also the difficulties of judging when the rising column of mercury had reached the highest point, due to the very slow movement which occurred in that region, and of getting satisfactory readings, owing to the short time that elapsed before a fall took place. The idea of following strictly the Hortvet technique, as regards stirring, for these particular experiments was therefore abandoned. In the first series of experiments, the results of which are recorded in Table 111, four or five stirrings of three strokes each were employed, and in the second series the mechanical stirrer, working at the rate of 40 strokes per minute, was in operation all the time, the thermometer rising until tapping became necessary.It does not appear that these variations in stirring caused any significant differences in the results obtained, but the times of rising of the mercury, after two different extents, large and small,OF MILK: CORRECTION FACTORS AND THE INFLUENCE OF STIRRING: I1 h I11 225 It was originally intended to employ four different amounts of supercooling for each sample of milk, vix. about 1.5, 1.0,0.8, and 0.5" C. It was found, however, that the differences in the readings of the thermometer corresponding to these different amounts of supercooling were in the neighbourhood of 0.002"-an amount so small that the unavoidable errors of observation might possibly approach the same order. It was, therefore, decided to employ only two different amounts of supercooling, as widely apart as practicable, say about 1.5" and 04", and to increase the number of samples examined.It was stated by Hortvet that, unless a much greater amount of supercooling than 0.5" is employed in the use of his cryoscope and technique, the rise of the mercury column is not sufficiently pronounced, and that there is more or less wavering, so that difficulty arises in deciding on the exact point at which the top of the column becomes stationary. Elsdon and Stubbs (Eoc. it.)^ found the same result when using a supercooling of less than about 0.8"; the mercury rose very slowly, and did not maintain a steady position for any appreciable time, and the proper freezing-point might not, under these circumstances, be attained. In the first experiments, made with the object of ascertaining the super- cooling correction, it was observed that where the amount of supercooling was small, that is, less than say 0-75", even in the absence of alcohol in the jacket surrounding the freezing-tube, the rise of temperature, when freezing occurred, was very slow-so slow, indeed, as to suggest doubts whether the thermometer would indicate the freezing-point of the milk, influenced only by supercooling, owing to the reading being affected by the length of time which elapses and the possibility of imperfect thermal insulation, causing a nett loss of heat from the freezing tube and contents.To give an instance; in an experiment when the supercooling was 0-71" the time required for the mercury column to rise until, on observation through the telescope with the aid of the horizontal cross-wire, the ascent became imperceptible, was 92 minutes, as compared with about 3& minutes when the same milk was super- cooled 1-49'.It will be seen later that, in the absence of alcohol in the space surrounding the freezing-tube, the heat insulation of the milk is not perfect; a nett loss of heat occurs, for it is possible t o carry through a freezing-point determination under such conditions. The difference between the two methods of working- with and without alcohol-results in a longer time being required for the cooling of the milk when the space around the freezing-tube is occupied by air. There were also the difficulties of judging when the rising column of mercury had reached the highest point, due to the very slow movement which occurred in that region, and of getting satisfactory readings, owing to the short time that elapsed before a fall took place.The idea of following strictly the Hortvet technique, as regards stirring, for these particular experiments was therefore abandoned. In the first series of experiments, the results of which are recorded in Table 111, four or five stirrings of three strokes each were employed, and in the second series the mechanical stirrer, working at the rate of 40 strokes per minute, was in operation all the time, the thermometer rising until tapping became necessary. It does not appear that these variations in stirring caused any significant differences in the results obtained, but the times of rising of the mercury, after two different extents, large and small,OF MILK: CORRECTION FACTORS AND THE INFLUENCE OF STIRRING: I1 h I11 225 It was originally intended to employ four different amounts of supercooling for each sample of milk, vix. about 1.5, 1.0,0.8, and 0.5" C.It was found, however, that the differences in the readings of the thermometer corresponding to these different amounts of supercooling were in the neighbourhood of 0.002"-an amount so small that the unavoidable errors of observation might possibly approach the same order. It was, therefore, decided to employ only two different amounts of supercooling, as widely apart as practicable, say about 1.5" and 04", and to increase the number of samples examined.It was stated by Hortvet that, unless a much greater amount of supercooling than 0.5" is employed in the use of his cryoscope and technique, the rise of the mercury column is not sufficiently pronounced, and that there is more or less wavering, so that difficulty arises in deciding on the exact point at which the top of the column becomes stationary. Elsdon and Stubbs (Eoc. it.)^ found the same result when using a supercooling of less than about 0.8"; the mercury rose very slowly, and did not maintain a steady position for any appreciable time, and the proper freezing-point might not, under these circumstances, be attained. In the first experiments, made with the object of ascertaining the super- cooling correction, it was observed that where the amount of supercooling was small, that is, less than say 0-75", even in the absence of alcohol in the jacket surrounding the freezing-tube, the rise of temperature, when freezing occurred, was very slow-so slow, indeed, as to suggest doubts whether the thermometer would indicate the freezing-point of the milk, influenced only by supercooling, owing to the reading being affected by the length of time which elapses and the possibility of imperfect thermal insulation, causing a nett loss of heat from the freezing tube and contents.To give an instance; in an experiment when the supercooling was 0-71" the time required for the mercury column to rise until, on observation through the telescope with the aid of the horizontal cross-wire, the ascent became imperceptible, was 92 minutes, as compared with about 3& minutes when the same milk was super- cooled 1-49'.It will be seen later that, in the absence of alcohol in the space surrounding the freezing-tube, the heat insulation of the milk is not perfect; a nett loss of heat occurs, for it is possible t o carry through a freezing-point determination under such conditions. The difference between the two methods of working- with and without alcohol-results in a longer time being required for the cooling of the milk when the space around the freezing-tube is occupied by air. There were also the difficulties of judging when the rising column of mercury had reached the highest point, due to the very slow movement which occurred in that region, and of getting satisfactory readings, owing to the short time that elapsed before a fall took place.The idea of following strictly the Hortvet technique, as regards stirring, for these particular experiments was therefore abandoned. In the first series of experiments, the results of which are recorded in Table 111, four or five stirrings of three strokes each were employed, and in the second series the mechanical stirrer, working at the rate of 40 strokes per minute, was in operation all the time, the thermometer rising until tapping became necessary. It does not appear that these variations in stirring caused any significant differences in the results obtained, but the times of rising of the mercury, after two different extents, large and small,OF MILK: CORRECTION FACTORS AND THE INFLUENCE OF STIRRING: I1 h I11 225 It was originally intended to employ four different amounts of supercooling for each sample of milk, vix.about 1.5, 1.0,0.8, and 0.5" C. It was found, however, that the differences in the readings of the thermometer corresponding to these different amounts of supercooling were in the neighbourhood of 0.002"-an amount so small that the unavoidable errors of observation might possibly approach the same order. It was, therefore, decided to employ only two different amounts of supercooling, as widely apart as practicable, say about 1.5" and 04", and to increase the number of samples examined. It was stated by Hortvet that, unless a much greater amount of supercooling than 0.5" is employed in the use of his cryoscope and technique, the rise of the mercury column is not sufficiently pronounced, and that there is more or less wavering, so that difficulty arises in deciding on the exact point at which the top of the column becomes stationary.Elsdon and Stubbs (Eoc. it.)^ found the same result when using a supercooling of less than about 0.8"; the mercury rose very slowly, and did not maintain a steady position for any appreciable time, and the proper freezing-point might not, under these circumstances, be attained. In the first experiments, made with the object of ascertaining the super- cooling correction, it was observed that where the amount of supercooling was small, that is, less than say 0-75", even in the absence of alcohol in the jacket surrounding the freezing-tube, the rise of temperature, when freezing occurred, was very slow-so slow, indeed, as to suggest doubts whether the thermometer would indicate the freezing-point of the milk, influenced only by supercooling, owing to the reading being affected by the length of time which elapses and the possibility of imperfect thermal insulation, causing a nett loss of heat from the freezing tube and contents.To give an instance; in an experiment when the supercooling was 0-71" the time required for the mercury column to rise until, on observation through the telescope with the aid of the horizontal cross-wire, the ascent became imperceptible, was 92 minutes, as compared with about 3& minutes when the same milk was super- cooled 1-49'. It will be seen later that, in the absence of alcohol in the space surrounding the freezing-tube, the heat insulation of the milk is not perfect; a nett loss of heat occurs, for it is possible t o carry through a freezing-point determination under such conditions. The difference between the two methods of working- with and without alcohol-results in a longer time being required for the cooling of the milk when the space around the freezing-tube is occupied by air.There were also the difficulties of judging when the rising column of mercury had reached the highest point, due to the very slow movement which occurred in that region, and of getting satisfactory readings, owing to the short time that elapsed before a fall took place. The idea of following strictly the Hortvet technique, as regards stirring, for these particular experiments was therefore abandoned.In the first series of experiments, the results of which are recorded in Table 111, four or five stirrings of three strokes each were employed, and in the second series the mechanical stirrer, working at the rate of 40 strokes per minute, was in operation all the time, the thermometer rising until tapping became necessary. It does not appear that these variations in stirring caused any significant differences in the results obtained, but the times of rising of the mercury, after two different extents, large and small,OF MILK: CORRECTION FACTORS AND THE INFLUENCE OF STIRRING: I1 h I11 225 It was originally intended to employ four different amounts of supercooling for each sample of milk, vix. about 1.5, 1.0,0.8, and 0.5" C. It was found, however, that the differences in the readings of the thermometer corresponding to these different amounts of supercooling were in the neighbourhood of 0.002"-an amount so small that the unavoidable errors of observation might possibly approach the same order.It was, therefore, decided to employ only two different amounts of supercooling, as widely apart as practicable, say about 1.5" and 04", and to increase the number of samples examined. It was stated by Hortvet that, unless a much greater amount of supercooling than 0.5" is employed in the use of his cryoscope and technique, the rise of the mercury column is not sufficiently pronounced, and that there is more or less wavering, so that difficulty arises in deciding on the exact point at which the top of the column becomes stationary.Elsdon and Stubbs (Eoc. it.)^ found the same result when using a supercooling of less than about 0.8"; the mercury rose very slowly, and did not maintain a steady position for any appreciable time, and the proper freezing-point might not, under these circumstances, be attained. In the first experiments, made with the object of ascertaining the super- cooling correction, it was observed that where the amount of supercooling was small, that is, less than say 0-75", even in the absence of alcohol in the jacket surrounding the freezing-tube, the rise of temperature, when freezing occurred, was very slow-so slow, indeed, as to suggest doubts whether the thermometer would indicate the freezing-point of the milk, influenced only by supercooling, owing to the reading being affected by the length of time which elapses and the possibility of imperfect thermal insulation, causing a nett loss of heat from the freezing tube and contents.To give an instance; in an experiment when the supercooling was 0-71" the time required for the mercury column to rise until, on observation through the telescope with the aid of the horizontal cross-wire, the ascent became imperceptible, was 92 minutes, as compared with about 3& minutes when the same milk was super- cooled 1-49'. It will be seen later that, in the absence of alcohol in the space surrounding the freezing-tube, the heat insulation of the milk is not perfect; a nett loss of heat occurs, for it is possible t o carry through a freezing-point determination under such conditions. The difference between the two methods of working- with and without alcohol-results in a longer time being required for the cooling of the milk when the space around the freezing-tube is occupied by air. There were also the difficulties of judging when the rising column of mercury had reached the highest point, due to the very slow movement which occurred in that region, and of getting satisfactory readings, owing to the short time that elapsed before a fall took place. The idea of following strictly the Hortvet technique, as regards stirring, for these particular experiments was therefore abandoned. In the first series of experiments, the results of which are recorded in Table 111, four or five stirrings of three strokes each were employed, and in the second series the mechanical stirrer, working at the rate of 40 strokes per minute, was in operation all the time, the thermometer rising until tapping became necessary. It does not appear that these variations in stirring caused any significant differences in the results obtained, but the times of rising of the mercury, after two different extents, large and small,

ISSN:0003-2654    

DOI:10.1039/AN9366100449

出版商:RSC    

年代:1936

数据来源: RSC

摘要:

OF MILK: CORRECTION FACTORS AND THE INFLUENCE OF STIRRING: I1 h I11 225 It was originally intended to employ four different amounts of supercooling for each sample of milk, vix. about 1.5, 1.0,0.8, and 0.5" C. It was found, however, that the differences in the readings of the thermometer corresponding to these different amounts of supercooling were in the neighbourhood of 0.002"-an amount so small that the unavoidable errors of observation might possibly approach the same order. It was, therefore, decided to employ only two different amounts of supercooling, as widely apart as practicable, say about 1.5" and 04", and to increase the number of samples examined. It was stated by Hortvet that, unless a much greater amount of supercooling than 0.5" is employed in the use of his cryoscope and technique, the rise of the mercury column is not sufficiently pronounced, and that there is more or less wavering, so that difficulty arises in deciding on the exact point at which the top of the column becomes stationary. Elsdon and Stubbs (Eoc.it.)^ found the same result when using a supercooling of less than about 0.8"; the mercury rose very slowly, and did not maintain a steady position for any appreciable time, and the proper freezing-point might not, under these circumstances, be attained. In the first experiments, made with the object of ascertaining the super- cooling correction, it was observed that where the amount of supercooling was small, that is, less than say 0-75", even in the absence of alcohol in the jacket surrounding the freezing-tube, the rise of temperature, when freezing occurred, was very slow-so slow, indeed, as to suggest doubts whether the thermometer would indicate the freezing-point of the milk, influenced only by supercooling, owing to the reading being affected by the length of time which elapses and the possibility of imperfect thermal insulation, causing a nett loss of heat from the freezing tube and contents.To give an instance; in an experiment when the supercooling was 0-71" the time required for the mercury column to rise until, on observation through the telescope with the aid of the horizontal cross-wire, the ascent became imperceptible, was 92 minutes, as compared with about 3& minutes when the same milk was super- cooled 1-49'. It will be seen later that, in the absence of alcohol in the space surrounding the freezing-tube, the heat insulation of the milk is not perfect; a nett loss of heat occurs, for it is possible t o carry through a freezing-point determination under such conditions.The difference between the two methods of working- with and without alcohol-results in a longer time being required for the cooling of the milk when the space around the freezing-tube is occupied by air. There were also the difficulties of judging when the rising column of mercury had reached the highest point, due to the very slow movement which occurred in that region, and of getting satisfactory readings, owing to the short time that elapsed before a fall took place. The idea of following strictly the Hortvet technique, as regards stirring, for these particular experiments was therefore abandoned.In the first series of experiments, the results of which are recorded in Table 111, four or five stirrings of three strokes each were employed, and in the second series the mechanical stirrer, working at the rate of 40 strokes per minute, was in operation all the time, the thermometer rising until tapping became necessary. It does not appear that these variations in stirring caused any significant differences in the results obtained, but the times of rising of the mercury, after two different extents, large and small,OF MILK: CORRECTION FACTORS AND THE INFLUENCE OF STIRRING: I1 h I11 225 It was originally intended to employ four different amounts of supercooling for each sample of milk, vix.about 1.5, 1.0,0.8, and 0.5" C. It was found, however, that the differences in the readings of the thermometer corresponding to these different amounts of supercooling were in the neighbourhood of 0.002"-an amount so small that the unavoidable errors of observation might possibly approach the same order. It was, therefore, decided to employ only two different amounts of supercooling, as widely apart as practicable, say about 1.5" and 04", and to increase the number of samples examined. It was stated by Hortvet that, unless a much greater amount of supercooling than 0.5" is employed in the use of his cryoscope and technique, the rise of the mercury column is not sufficiently pronounced, and that there is more or less wavering, so that difficulty arises in deciding on the exact point at which the top of the column becomes stationary.Elsdon and Stubbs (Eoc. it.)^ found the same result when using a supercooling of less than about 0.8"; the mercury rose very slowly, and did not maintain a steady position for any appreciable time, and the proper freezing-point might not, under these circumstances, be attained. In the first experiments, made with the object of ascertaining the super- cooling correction, it was observed that where the amount of supercooling was small, that is, less than say 0-75", even in the absence of alcohol in the jacket surrounding the freezing-tube, the rise of temperature, when freezing occurred, was very slow-so slow, indeed, as to suggest doubts whether the thermometer would indicate the freezing-point of the milk, influenced only by supercooling, owing to the reading being affected by the length of time which elapses and the possibility of imperfect thermal insulation, causing a nett loss of heat from the freezing tube and contents.To give an instance; in an experiment when the supercooling was 0-71" the time required for the mercury column to rise until, on observation through the telescope with the aid of the horizontal cross-wire, the ascent became imperceptible, was 92 minutes, as compared with about 3& minutes when the same milk was super- cooled 1-49'. It will be seen later that, in the absence of alcohol in the space surrounding the freezing-tube, the heat insulation of the milk is not perfect; a nett loss of heat occurs, for it is possible t o carry through a freezing-point determination under such conditions.The difference between the two methods of working- with and without alcohol-results in a longer time being required for the cooling of the milk when the space around the freezing-tube is occupied by air. There were also the difficulties of judging when the rising column of mercury had reached the highest point, due to the very slow movement which occurred in that region, and of getting satisfactory readings, owing to the short time that elapsed before a fall took place. The idea of following strictly the Hortvet technique, as regards stirring, for these particular experiments was therefore abandoned. In the first series of experiments, the results of which are recorded in Table 111, four or five stirrings of three strokes each were employed, and in the second series the mechanical stirrer, working at the rate of 40 strokes per minute, was in operation all the time, the thermometer rising until tapping became necessary.It does not appear that these variations in stirring caused any significant differences in the results obtained, but the times of rising of the mercury, after two different extents, large and small,OF MILK: CORRECTION FACTORS AND THE INFLUENCE OF STIRRING: I1 h I11 225 It was originally intended to employ four different amounts of supercooling for each sample of milk, vix. about 1.5, 1.0,0.8, and 0.5" C. It was found, however, that the differences in the readings of the thermometer corresponding to these different amounts of supercooling were in the neighbourhood of 0.002"-an amount so small that the unavoidable errors of observation might possibly approach the same order.It was, therefore, decided to employ only two different amounts of supercooling, as widely apart as practicable, say about 1.5" and 04", and to increase the number of samples examined. It was stated by Hortvet that, unless a much greater amount of supercooling than 0.5" is employed in the use of his cryoscope and technique, the rise of the mercury column is not sufficiently pronounced, and that there is more or less wavering, so that difficulty arises in deciding on the exact point at which the top of the column becomes stationary. Elsdon and Stubbs (Eoc. it.)^ found the same result when using a supercooling of less than about 0.8"; the mercury rose very slowly, and did not maintain a steady position for any appreciable time, and the proper freezing-point might not, under these circumstances, be attained.In the first experiments, made with the object of ascertaining the super- cooling correction, it was observed that where the amount of supercooling was small, that is, less than say 0-75", even in the absence of alcohol in the jacket surrounding the freezing-tube, the rise of temperature, when freezing occurred, was very slow-so slow, indeed, as to suggest doubts whether the thermometer would indicate the freezing-point of the milk, influenced only by supercooling, owing to the reading being affected by the length of time which elapses and the possibility of imperfect thermal insulation, causing a nett loss of heat from the freezing tube and contents. To give an instance; in an experiment when the supercooling was 0-71" the time required for the mercury column to rise until, on observation through the telescope with the aid of the horizontal cross-wire, the ascent became imperceptible, was 92 minutes, as compared with about 3& minutes when the same milk was super- cooled 1-49'.It will be seen later that, in the absence of alcohol in the space surrounding the freezing-tube, the heat insulation of the milk is not perfect; a nett loss of heat occurs, for it is possible t o carry through a freezing-point determination under such conditions. The difference between the two methods of working- with and without alcohol-results in a longer time being required for the cooling of the milk when the space around the freezing-tube is occupied by air.There were also the difficulties of judging when the rising column of mercury had reached the highest point, due to the very slow movement which occurred in that region, and of getting satisfactory readings, owing to the short time that elapsed before a fall took place. The idea of following strictly the Hortvet technique, as regards stirring, for these particular experiments was therefore abandoned. In the first series of experiments, the results of which are recorded in Table 111, four or five stirrings of three strokes each were employed, and in the second series the mechanical stirrer, working at the rate of 40 strokes per minute, was in operation all the time, the thermometer rising until tapping became necessary.It does not appear that these variations in stirring caused any significant differences in the results obtained, but the times of rising of the mercury, after two different extents, large and small,OF MILK: CORRECTION FACTORS AND THE INFLUENCE OF STIRRING: I1 h I11 225 It was originally intended to employ four different amounts of supercooling for each sample of milk, vix. about 1.5, 1.0,0.8, and 0.5" C. It was found, however, that the differences in the readings of the thermometer corresponding to these different amounts of supercooling were in the neighbourhood of 0.002"-an amount so small that the unavoidable errors of observation might possibly approach the same order. It was, therefore, decided to employ only two different amounts of supercooling, as widely apart as practicable, say about 1.5" and 04", and to increase the number of samples examined.It was stated by Hortvet that, unless a much greater amount of supercooling than 0.5" is employed in the use of his cryoscope and technique, the rise of the mercury column is not sufficiently pronounced, and that there is more or less wavering, so that difficulty arises in deciding on the exact point at which the top of the column becomes stationary. Elsdon and Stubbs (Eoc. it.)^ found the same result when using a supercooling of less than about 0.8"; the mercury rose very slowly, and did not maintain a steady position for any appreciable time, and the proper freezing-point might not, under these circumstances, be attained. In the first experiments, made with the object of ascertaining the super- cooling correction, it was observed that where the amount of supercooling was small, that is, less than say 0-75", even in the absence of alcohol in the jacket surrounding the freezing-tube, the rise of temperature, when freezing occurred, was very slow-so slow, indeed, as to suggest doubts whether the thermometer would indicate the freezing-point of the milk, influenced only by supercooling, owing to the reading being affected by the length of time which elapses and the possibility of imperfect thermal insulation, causing a nett loss of heat from the freezing tube and contents.To give an instance; in an experiment when the supercooling was 0-71" the time required for the mercury column to rise until, on observation through the telescope with the aid of the horizontal cross-wire, the ascent became imperceptible, was 92 minutes, as compared with about 3& minutes when the same milk was super- cooled 1-49'.It will be seen later that, in the absence of alcohol in the space surrounding the freezing-tube, the heat insulation of the milk is not perfect; a nett loss of heat occurs, for it is possible t o carry through a freezing-point determination under such conditions. The difference between the two methods of working- with and without alcohol-results in a longer time being required for the cooling of the milk when the space around the freezing-tube is occupied by air. There were also the difficulties of judging when the rising column of mercury had reached the highest point, due to the very slow movement which occurred in that region, and of getting satisfactory readings, owing to the short time that elapsed before a fall took place. The idea of following strictly the Hortvet technique, as regards stirring, for these particular experiments was therefore abandoned. In the first series of experiments, the results of which are recorded in Table 111, four or five stirrings of three strokes each were employed, and in the second series the mechanical stirrer, working at the rate of 40 strokes per minute, was in operation all the time, the thermometer rising until tapping became necessary. It does not appear that these variations in stirring caused any significant differences in the results obtained, but the times of rising of the mercury, after two different extents, large and small,

ISSN:0003-2654    

DOI:10.1039/AN9366100455

出版商:RSC    

年代:1936

数据来源: RSC

摘要:

OF MILK: CORRECTION FACTORS AND THE INFLUENCE OF STIRRING: I1 h I11 225 It was originally intended to employ four different amounts of supercooling for each sample of milk, vix. about 1.5, 1.0,0.8, and 0.5" C. It was found, however, that the differences in the readings of the thermometer corresponding to these different amounts of supercooling were in the neighbourhood of 0.002"-an amount so small that the unavoidable errors of observation might possibly approach the same order. It was, therefore, decided to employ only two different amounts of supercooling, as widely apart as practicable, say about 1.5" and 04", and to increase the number of samples examined. It was stated by Hortvet that, unless a much greater amount of supercooling than 0.5" is employed in the use of his cryoscope and technique, the rise of the mercury column is not sufficiently pronounced, and that there is more or less wavering, so that difficulty arises in deciding on the exact point at which the top of the column becomes stationary. Elsdon and Stubbs (Eoc.it.)^ found the same result when using a supercooling of less than about 0.8"; the mercury rose very slowly, and did not maintain a steady position for any appreciable time, and the proper freezing-point might not, under these circumstances, be attained. In the first experiments, made with the object of ascertaining the super- cooling correction, it was observed that where the amount of supercooling was small, that is, less than say 0-75", even in the absence of alcohol in the jacket surrounding the freezing-tube, the rise of temperature, when freezing occurred, was very slow-so slow, indeed, as to suggest doubts whether the thermometer would indicate the freezing-point of the milk, influenced only by supercooling, owing to the reading being affected by the length of time which elapses and the possibility of imperfect thermal insulation, causing a nett loss of heat from the freezing tube and contents.To give an instance; in an experiment when the supercooling was 0-71" the time required for the mercury column to rise until, on observation through the telescope with the aid of the horizontal cross-wire, the ascent became imperceptible, was 92 minutes, as compared with about 3& minutes when the same milk was super- cooled 1-49'. It will be seen later that, in the absence of alcohol in the space surrounding the freezing-tube, the heat insulation of the milk is not perfect; a nett loss of heat occurs, for it is possible t o carry through a freezing-point determination under such conditions.The difference between the two methods of working- with and without alcohol-results in a longer time being required for the cooling of the milk when the space around the freezing-tube is occupied by air. There were also the difficulties of judging when the rising column of mercury had reached the highest point, due to the very slow movement which occurred in that region, and of getting satisfactory readings, owing to the short time that elapsed before a fall took place. The idea of following strictly the Hortvet technique, as regards stirring, for these particular experiments was therefore abandoned.In the first series of experiments, the results of which are recorded in Table 111, four or five stirrings of three strokes each were employed, and in the second series the mechanical stirrer, working at the rate of 40 strokes per minute, was in operation all the time, the thermometer rising until tapping became necessary. It does not appear that these variations in stirring caused any significant differences in the results obtained, but the times of rising of the mercury, after two different extents, large and small,OF MILK: CORRECTION FACTORS AND THE INFLUENCE OF STIRRING: I1 h I11 225 It was originally intended to employ four different amounts of supercooling for each sample of milk, vix.about 1.5, 1.0,0.8, and 0.5" C. It was found, however, that the differences in the readings of the thermometer corresponding to these different amounts of supercooling were in the neighbourhood of 0.002"-an amount so small that the unavoidable errors of observation might possibly approach the same order. It was, therefore, decided to employ only two different amounts of supercooling, as widely apart as practicable, say about 1.5" and 04", and to increase the number of samples examined. It was stated by Hortvet that, unless a much greater amount of supercooling than 0.5" is employed in the use of his cryoscope and technique, the rise of the mercury column is not sufficiently pronounced, and that there is more or less wavering, so that difficulty arises in deciding on the exact point at which the top of the column becomes stationary.Elsdon and Stubbs (Eoc. it.)^ found the same result when using a supercooling of less than about 0.8"; the mercury rose very slowly, and did not maintain a steady position for any appreciable time, and the proper freezing-point might not, under these circumstances, be attained. In the first experiments, made with the object of ascertaining the super- cooling correction, it was observed that where the amount of supercooling was small, that is, less than say 0-75", even in the absence of alcohol in the jacket surrounding the freezing-tube, the rise of temperature, when freezing occurred, was very slow-so slow, indeed, as to suggest doubts whether the thermometer would indicate the freezing-point of the milk, influenced only by supercooling, owing to the reading being affected by the length of time which elapses and the possibility of imperfect thermal insulation, causing a nett loss of heat from the freezing tube and contents.To give an instance; in an experiment when the supercooling was 0-71" the time required for the mercury column to rise until, on observation through the telescope with the aid of the horizontal cross-wire, the ascent became imperceptible, was 92 minutes, as compared with about 3& minutes when the same milk was super- cooled 1-49'. It will be seen later that, in the absence of alcohol in the space surrounding the freezing-tube, the heat insulation of the milk is not perfect; a nett loss of heat occurs, for it is possible t o carry through a freezing-point determination under such conditions.The difference between the two methods of working- with and without alcohol-results in a longer time being required for the cooling of the milk when the space around the freezing-tube is occupied by air. There were also the difficulties of judging when the rising column of mercury had reached the highest point, due to the very slow movement which occurred in that region, and of getting satisfactory readings, owing to the short time that elapsed before a fall took place. The idea of following strictly the Hortvet technique, as regards stirring, for these particular experiments was therefore abandoned. In the first series of experiments, the results of which are recorded in Table 111, four or five stirrings of three strokes each were employed, and in the second series the mechanical stirrer, working at the rate of 40 strokes per minute, was in operation all the time, the thermometer rising until tapping became necessary.It does not appear that these variations in stirring caused any significant differences in the results obtained, but the times of rising of the mercury, after two different extents, large and small,OF MILK: CORRECTION FACTORS AND THE INFLUENCE OF STIRRING: I1 h I11 225 It was originally intended to employ four different amounts of supercooling for each sample of milk, vix. about 1.5, 1.0,0.8, and 0.5" C. It was found, however, that the differences in the readings of the thermometer corresponding to these different amounts of supercooling were in the neighbourhood of 0.002"-an amount so small that the unavoidable errors of observation might possibly approach the same order.It was, therefore, decided to employ only two different amounts of supercooling, as widely apart as practicable, say about 1.5" and 04", and to increase the number of samples examined. It was stated by Hortvet that, unless a much greater amount of supercooling than 0.5" is employed in the use of his cryoscope and technique, the rise of the mercury column is not sufficiently pronounced, and that there is more or less wavering, so that difficulty arises in deciding on the exact point at which the top of the column becomes stationary. Elsdon and Stubbs (Eoc. it.)^ found the same result when using a supercooling of less than about 0.8"; the mercury rose very slowly, and did not maintain a steady position for any appreciable time, and the proper freezing-point might not, under these circumstances, be attained.In the first experiments, made with the object of ascertaining the super- cooling correction, it was observed that where the amount of supercooling was small, that is, less than say 0-75", even in the absence of alcohol in the jacket surrounding the freezing-tube, the rise of temperature, when freezing occurred, was very slow-so slow, indeed, as to suggest doubts whether the thermometer would indicate the freezing-point of the milk, influenced only by supercooling, owing to the reading being affected by the length of time which elapses and the possibility of imperfect thermal insulation, causing a nett loss of heat from the freezing tube and contents. To give an instance; in an experiment when the supercooling was 0-71" the time required for the mercury column to rise until, on observation through the telescope with the aid of the horizontal cross-wire, the ascent became imperceptible, was 92 minutes, as compared with about 3& minutes when the same milk was super- cooled 1-49'.It will be seen later that, in the absence of alcohol in the space surrounding the freezing-tube, the heat insulation of the milk is not perfect; a nett loss of heat occurs, for it is possible t o carry through a freezing-point determination under such conditions. The difference between the two methods of working- with and without alcohol-results in a longer time being required for the cooling of the milk when the space around the freezing-tube is occupied by air.There were also the difficulties of judging when the rising column of mercury had reached the highest point, due to the very slow movement which occurred in that region, and of getting satisfactory readings, owing to the short time that elapsed before a fall took place. The idea of following strictly the Hortvet technique, as regards stirring, for these particular experiments was therefore abandoned. In the first series of experiments, the results of which are recorded in Table 111, four or five stirrings of three strokes each were employed, and in the second series the mechanical stirrer, working at the rate of 40 strokes per minute, was in operation all the time, the thermometer rising until tapping became necessary.It does not appear that these variations in stirring caused any significant differences in the results obtained, but the times of rising of the mercury, after two different extents, large and small,OF MILK: CORRECTION FACTORS AND THE INFLUENCE OF STIRRING: I1 h I11 225 It was originally intended to employ four different amounts of supercooling for each sample of milk, vix. about 1.5, 1.0,0.8, and 0.5" C. It was found, however, that the differences in the readings of the thermometer corresponding to these different amounts of supercooling were in the neighbourhood of 0.002"-an amount so small that the unavoidable errors of observation might possibly approach the same order. It was, therefore, decided to employ only two different amounts of supercooling, as widely apart as practicable, say about 1.5" and 04", and to increase the number of samples examined.It was stated by Hortvet that, unless a much greater amount of supercooling than 0.5" is employed in the use of his cryoscope and technique, the rise of the mercury column is not sufficiently pronounced, and that there is more or less wavering, so that difficulty arises in deciding on the exact point at which the top of the column becomes stationary. Elsdon and Stubbs (Eoc. it.)^ found the same result when using a supercooling of less than about 0.8"; the mercury rose very slowly, and did not maintain a steady position for any appreciable time, and the proper freezing-point might not, under these circumstances, be attained. In the first experiments, made with the object of ascertaining the super- cooling correction, it was observed that where the amount of supercooling was small, that is, less than say 0-75", even in the absence of alcohol in the jacket surrounding the freezing-tube, the rise of temperature, when freezing occurred, was very slow-so slow, indeed, as to suggest doubts whether the thermometer would indicate the freezing-point of the milk, influenced only by supercooling, owing to the reading being affected by the length of time which elapses and the possibility of imperfect thermal insulation, causing a nett loss of heat from the freezing tube and contents.To give an instance; in an experiment when the supercooling was 0-71" the time required for the mercury column to rise until, on observation through the telescope with the aid of the horizontal cross-wire, the ascent became imperceptible, was 92 minutes, as compared with about 3& minutes when the same milk was super- cooled 1-49'.It will be seen later that, in the absence of alcohol in the space surrounding the freezing-tube, the heat insulation of the milk is not perfect; a nett loss of heat occurs, for it is possible t o carry through a freezing-point determination under such conditions. The difference between the two methods of working- with and without alcohol-results in a longer time being required for the cooling of the milk when the space around the freezing-tube is occupied by air. There were also the difficulties of judging when the rising column of mercury had reached the highest point, due to the very slow movement which occurred in that region, and of getting satisfactory readings, owing to the short time that elapsed before a fall took place.The idea of following strictly the Hortvet technique, as regards stirring, for these particular experiments was therefore abandoned. In the first series of experiments, the results of which are recorded in Table 111, four or five stirrings of three strokes each were employed, and in the second series the mechanical stirrer, working at the rate of 40 strokes per minute, was in operation all the time, the thermometer rising until tapping became necessary. It does not appear that these variations in stirring caused any significant differences in the results obtained, but the times of rising of the mercury, after two different extents, large and small,OF MILK: CORRECTION FACTORS AND THE INFLUENCE OF STIRRING: I1 h I11 225 It was originally intended to employ four different amounts of supercooling for each sample of milk, vix. about 1.5, 1.0,0.8, and 0.5" C.It was found, however, that the differences in the readings of the thermometer corresponding to these different amounts of supercooling were in the neighbourhood of 0.002"-an amount so small that the unavoidable errors of observation might possibly approach the same order. It was, therefore, decided to employ only two different amounts of supercooling, as widely apart as practicable, say about 1.5" and 04", and to increase the number of samples examined.It was stated by Hortvet that, unless a much greater amount of supercooling than 0.5" is employed in the use of his cryoscope and technique, the rise of the mercury column is not sufficiently pronounced, and that there is more or less wavering, so that difficulty arises in deciding on the exact point at which the top of the column becomes stationary. Elsdon and Stubbs (Eoc. it.)^ found the same result when using a supercooling of less than about 0.8"; the mercury rose very slowly, and did not maintain a steady position for any appreciable time, and the proper freezing-point might not, under these circumstances, be attained. In the first experiments, made with the object of ascertaining the super- cooling correction, it was observed that where the amount of supercooling was small, that is, less than say 0-75", even in the absence of alcohol in the jacket surrounding the freezing-tube, the rise of temperature, when freezing occurred, was very slow-so slow, indeed, as to suggest doubts whether the thermometer would indicate the freezing-point of the milk, influenced only by supercooling, owing to the reading being affected by the length of time which elapses and the possibility of imperfect thermal insulation, causing a nett loss of heat from the freezing tube and contents.To give an instance; in an experiment when the supercooling was 0-71" the time required for the mercury column to rise until, on observation through the telescope with the aid of the horizontal cross-wire, the ascent became imperceptible, was 92 minutes, as compared with about 3& minutes when the same milk was super- cooled 1-49'.It will be seen later that, in the absence of alcohol in the space surrounding the freezing-tube, the heat insulation of the milk is not perfect; a nett loss of heat occurs, for it is possible t o carry through a freezing-point determination under such conditions. The difference between the two methods of working- with and without alcohol-results in a longer time being required for the cooling of the milk when the space around the freezing-tube is occupied by air. There were also the difficulties of judging when the rising column of mercury had reached the highest point, due to the very slow movement which occurred in that region, and of getting satisfactory readings, owing to the short time that elapsed before a fall took place.The idea of following strictly the Hortvet technique, as regards stirring, for these particular experiments was therefore abandoned. In the first series of experiments, the results of which are recorded in Table 111, four or five stirrings of three strokes each were employed, and in the second series the mechanical stirrer, working at the rate of 40 strokes per minute, was in operation all the time, the thermometer rising until tapping became necessary. It does not appear that these variations in stirring caused any significant differences in the results obtained, but the times of rising of the mercury, after two different extents, large and small,OF MILK: CORRECTION FACTORS AND THE INFLUENCE OF STIRRING: I1 h I11 225 It was originally intended to employ four different amounts of supercooling for each sample of milk, vix.about 1.5, 1.0,0.8, and 0.5" C. It was found, however, that the differences in the readings of the thermometer corresponding to these different amounts of supercooling were in the neighbourhood of 0.002"-an amount so small that the unavoidable errors of observation might possibly approach the same order. It was, therefore, decided to employ only two different amounts of supercooling, as widely apart as practicable, say about 1.5" and 04", and to increase the number of samples examined. It was stated by Hortvet that, unless a much greater amount of supercooling than 0.5" is employed in the use of his cryoscope and technique, the rise of the mercury column is not sufficiently pronounced, and that there is more or less wavering, so that difficulty arises in deciding on the exact point at which the top of the column becomes stationary.Elsdon and Stubbs (Eoc. it.)^ found the same result when using a supercooling of less than about 0.8"; the mercury rose very slowly, and did not maintain a steady position for any appreciable time, and the proper freezing-point might not, under these circumstances, be attained. In the first experiments, made with the object of ascertaining the super- cooling correction, it was observed that where the amount of supercooling was small, that is, less than say 0-75", even in the absence of alcohol in the jacket surrounding the freezing-tube, the rise of temperature, when freezing occurred, was very slow-so slow, indeed, as to suggest doubts whether the thermometer would indicate the freezing-point of the milk, influenced only by supercooling, owing to the reading being affected by the length of time which elapses and the possibility of imperfect thermal insulation, causing a nett loss of heat from the freezing tube and contents.To give an instance; in an experiment when the supercooling was 0-71" the time required for the mercury column to rise until, on observation through the telescope with the aid of the horizontal cross-wire, the ascent became imperceptible, was 92 minutes, as compared with about 3& minutes when the same milk was super- cooled 1-49'. It will be seen later that, in the absence of alcohol in the space surrounding the freezing-tube, the heat insulation of the milk is not perfect; a nett loss of heat occurs, for it is possible t o carry through a freezing-point determination under such conditions. The difference between the two methods of working- with and without alcohol-results in a longer time being required for the cooling of the milk when the space around the freezing-tube is occupied by air. There were also the difficulties of judging when the rising column of mercury had reached the highest point, due to the very slow movement which occurred in that region, and of getting satisfactory readings, owing to the short time that elapsed before a fall took place. The idea of following strictly the Hortvet technique, as regards stirring, for these particular experiments was therefore abandoned. In the first series of experiments, the results of which are recorded in Table 111, four or five stirrings of three strokes each were employed, and in the second series the mechanical stirrer, working at the rate of 40 strokes per minute, was in operation all the time, the thermometer rising until tapping became necessary. It does not appear that these variations in stirring caused any significant differences in the results obtained, but the times of rising of the mercury, after two different extents, large and small,

ISSN:0003-2654    

DOI:10.1039/AN9366100459

出版商:RSC    

年代:1936

数据来源: RSC

摘要:

MORTON THE ESTIMATION OF LEAD IN URINE 465 The Application of Diphenyl Thiocarbazone (Dithizone) to the Estimation of Lead in Urine BY F. MORTON B.Sc. A.I.C. IT is generally accepted that if sufficiently sensitive qualitative tests are applied, such as the triple nitrite method (Fairhall),6 in which caesium nitrite is used at the final stage many normal urines will give positive results for lead. Various values for the amounts of lead in normal urines have been recorded by different workers; Kehoe and Thamann,ll from the analysis of urine of healthy students found an average value of 0.08 mg. per litre; Rabinowitch Dingwall and Mackay16 give 0.1 mg. per litre as an average; Francis Harvey and Buchan9 found values ranging from nil to 0.133 mg. per litre with an average of 0.04 mg.In an extensive series of investigations Kehoe Thamann and Cholak (1933)lS have shown that even certain primitive peoples living under conditions involving but the slightest intake of lead excreted in their urine very small amounts of the metal traceable to a minute amount of lead in the native soil. These investigators found generally, much larger amounts of lead in the excreta of people exposed industrially to the metal than in those of normal persons. The urinary differences between normal and lead-intoxicated persons are therefore determinable and as an aid to diagnosis quantitative investigations of available material need to be carried out. A review of the methods at present available for the estimation of lead in biological material indicates that few are acceptable for routine purposes in the clinical laboratory.Fairhall (1922)5 described a chromate method for lead in urine etc. which has been widely used in the original and modified forms during the last few years. Apart from the length of time required for the completion of these methods (4 t o 8 days) there is some doubt whether lead can be quantitatively precipitated as chromate under Fairhall’s conditions when less than 0.1 mg. of lead is present. Satisfactory recovery of added lead is reported by Myers, Gustafson and Throne,l4 who used a simple modification of Fairhall’s method but this has not been the experience in this laboratory. Kehoe et aZ.I2 in their investiga-tions employed an elaborate chromate method but a more recent publication by the same workerP discloses the occurrence of an approximately constant error of 0.07 mg.of lead per sample. This fact was only revealed when the chromate results were compared with those obtained by a spectrographic method (Cholak 1935).a For lead in urine Cooksey and Waltons (1929) have applied a process of direct electrolysis of the acidified sample the metal deposited on the anode being dissolved and deter-mined by a standard procedure. The method is simple and rapid but no evidence is provided to justify the assumption that all the lead in urine is in the ionised form. A much more elaborate electrolytic method of wider application requiring 3 to 4 days for completion has been described by Francis Harvey and B u ~ h a n . ~ Large amounts of reagents are required for the wet oxidation of the material; Two electrolytic methods have been described in recent years 466 MORTON THE APPLICATION OF DIPHENYL THIOCARBAZONE (DITHIZONE) this necessitates preliminary purification and together with the need of special expensive equipment makes the method unsuitable for laboratories where only occasional demand arises for lead estimations.A rapid method of lead estimation in urine providing reasonably accurate results seemed a need worthy of attention. The following aims have been kept in mind in developing such a method:-the volumes of reagents should be sinall to avoid the necessity for tedious processes of purification there should be reasonable precision and specificity and it should be possible to complete the estimation within approximately 24 hours of receiving the sample.A satisfactory procedure based on the separation of lead with diphenyl thiocarbazone has been worked out. The studies of Fischer' and of Fischer and Leopoldi8 have naturally led to the application of diphenyl thiocarbazone as an analytical reagent (Fischer,' Allport and Skrimshire? Bohnenkamp and Linneweh,2 1933). The technique of Allport and Skrimshirel was applied to the estimation of lead in urine and proved unsatisfactory in certain respects. First the process of wet oxidation of 500ml. of urine involves the use of fairly large amounts of reagents and is moreover a tedious task requiring considerable time and attention. Secondly the strength of their dithizone solution viz. 0-1 per cent. w/v was much too great when only small amounts of lead were to be separated; the bright green colour of the excess of reagent completely masked the pink colour of the lead derivative.This rendered it impossible to decide whether or not the last traces of lead had been removed; and furthermore the presence of a large excess of free dithizone added to the difficulty of bringing to satisfactory completion the sub-sequent wet oxidation of the chloroform extracts. Lastly the amount of cyanide used by Allport and Skrimshire in their extraction process was considered insufficient since on several occasions violet extracts were obtained from which the colour was discharged by shaking with an additional quantity of cyanide. METHOD REAGENTS REQUIRED. Dithizone Reagent.-A 0.05 per cent.solution of dithizone in chloroform is shaken with 10 per cent. ammonia in a separating funnel the chloroform solution being afterwards extracted with fresh supplies of ammonia until it no longer shows a green colour whereupon it is discarded. The ammoniacal extracts are united and acidified with dilute sulphuric acid in the separating funnel and the dithizone thereby precipitated is re-dissolved in pure chloroform to give an approxi-mately 0.05 per cent. solution. This solution is diluted with equal volumes of pure chloroform as required for application in the analytical procedure. The stronger solution is stored in a dark coloured bottle not exposed to sunlight. Under these conditions it appears to keep well for 2 to 3 weeks. Potassium cyanide A.R.-1 and 10 per cent.solutions. Ammonia A.R.-2 and 10 per cent. solutions. Ammonium citrate.-60 per cent. solution. Hydrochloric acid A.R.-10 per cent. and N/10 solutions. The above aqueous solutions are made up with doubly distilled water. ANALYTICAL PROCEDURE.-^^^^ ml. of urine are treated with 10 ml. of strong The phosphate precipitate ammonia solution and allowed to stand overnight TO THE ESTIMATION OF LEAD IN URINE 467 is filtered off on a No. 44 Whatman paper and Buchner funnel. The sides of the beaker are washed with a small amount of 2 per cent. ammonia which is poured into the filter-funnel only when nearly all the urine has passed through. Gentle suction is applied to the filter until the precipitate is dry. The precipitate together with the paper is then ashed for 1 hour in a silica basin in a muffle regulated at about 500" C.The dish is allowed to cool and the charred residue is treated with a few drops of conc. nitric acid after which it is re-heated for half-an-hour. The ash which should be almost white and free from carbon is cooled and dissolved in 20 ml. of 10 per cent. hydrochloric acid and the solution is boiled for a few minutes and filtered through a small paper. The dish and filter are washed 5 or 6 times with hot water. The filtrate and washings are cooled and 10ml. of 60 per cent. ammonium citrate solution followed by 5 ml. of 10 per cent. potassium cyanide solution are added. The liquid is then made just alkaline to litmus by the addition of 10 per cent. ammonia solution. A blank analysis of reagents is made at the same time.The alkaline solution which should be perfectly clear is transferred to a 300-ml. separating funnel and vigorously shaken with 5 ml. of the dilute dithizone solution. In the presence of lead the chlofoform is pink or violet according to the amount of the metal present. The separated chloroform layer is removed, and the aqueous solution is shaken with another 5 ml. of dithizone solution. The process of lead extraction is continued in this way until the separated chloroform layer shows no suggestion of a pink colour after it has been washed with a solution containing 5 ml. of 1 per cent. potassium cyanide and 5 ml. of 2 per cent. ammonia mixed with 10 ml. of distilled water. This washing solution removes the greater part of the excess of free dithizone and renders it far easier to decide whether the lead has been extracted completely.The combined chloroform extracts from the process still contain free dithizone, which must now be completely removed. The extract is placed in a small separat-ing funnel and shaken with several fresh additions of the alkaline cyanide wash-solution mentioned above. Some means of preventing loss of extract during the washing processes has to be adopted since chloroform is held in the surface of the aqueous layer. This can be done by mixing the wash-layers together finally separating the accumulated chloroform at the end of the washing process and returning it to the main bulk of extract. When the chloroform extract no longer contains free dithizone (as indicated by the clear and colourless appearance of the last cyanide wash-solution) it is washed with distilled water and returned to the clean separating funnel.I t is then shaken with 15 ml. of N/10 hydrochloric acid whereby the pink lead dithizone derivative is decomposed into the equivalent amounts of free dithizone and lead chloride. The former dissolves in the chloroform layer giving it a bright green colour whilst the lead is taken up by the acid layer. The green chloroform solution is transferred to a 50-ml. volumetric flask the acid layer being washed with re-distilled chloroform and these washings added to the solution in the standard flask. After being made up to the mark with chloroform the solution is ready for colori-metric measurement. This can be effected either by direct comparison against a standard colour prepared simultaneously with the unknown from a standard solutio 468 MORTON THE APPLICATION OF DIPHENYL THIOCARBAZONE (DITHIZONE) of lead or by measurements of its extinction coefficient with the Zeiss-Pulfrich photometer as described below.instrument eliminates the necessity of repeated preparation of standards for comparison and also enables one to investigate the validity of Beer's Law for the colou'r to be measured. A series of standard lead solutions was prepared and the lead extracted by the foregoing procedure. The chloroform extracts containing free dithizone were made up to 50ml. and the extinction coefficients measured for each of the light-filters provided with the instrument. On plotting the extinction coefficients against mean wave-length of the series of light-filters, dithizone in chloroform was found to possess a maximum light absorption in the region of 610mp.This corresponds with the findings of Bohnenkamp and Linneweh,2 who in a more elaborate study of the absorption spectrum of dithizone in carbon tetrachloride observed a maximum absorption at 630mp. The light-filter corresponding with the region of maximum absorption was used in measurements of extinction coefficients in subsequent analyses. The dithizone extinction coefficients observed with this filter were plotted against the corresponding lead-contents of the standard lead solutions and a curve indicating the direct proportionality existing between the lead and the dithizone with which it combines during the analytical procedure was obtained.COLORIMETRIC COMPARISON.-If the Zeiss instrument is not available a colorimeter can be applied either (i) by comparing the unknown with a standard prepared from a suitable lead solution extracted at the same time as the unknown solution or (ii) by comparison with a solution of dithizone in chloroform containing 1 mg. per 100 ml. The second suggestion is based on measurements of the extinc-tion coefficients of various concentrations of commercial dithizone dissolved in chloroform. The approximate absorption spectrum of such solutions corresponded with the curves previously obtained. It was also found that the colour of a solution of dithizone ( 1 mg. per 100 ml.) is equal in strength to that obtained from 0.09 mg. of lead when this is extracted by the above process and the final volume of such extract is made up to 50 ml.volume. Colorimetric comparison of weak solutions of dithizone must be made fairly rapidly since a tendency to fading has been observed on several occasions. The standard prepared from the commercial chemical must be made up freshly as required. of note that the foregoing procedure allows for a simple check on the analysis. After the lead dithizone extract has been shaken with acid at the final stage the lead actually remains behind in the acid layer. In a few instances the acid layer has been analysed for its lead-content by a sulphide method. For this purpose the acid solution is washed 3 to 4 times with chloroform to remove completely all traces of dithizone which would otherwise interfere with the subsequent sulphide comparison.The chloroform is removed and the solution remaining heated on a boiling water-bath for several minutes. After cooling the solution is made slightly alkaline with ammonia and 1 gm. of ammonium acetate followed CALIBRATION OF THE ZEISS-PULFRICH PHOTOMETER.-The use Of the Zeiss METHOD OF CHECKING RESULTS BY A SULPHIDE PROCEDURE.-It is worth TO THE ESTIMATION OF LEAD IN URINE 469 by 1 ml. of 10 per cent. sodium sulphide is added. The solution is then com-pared with suitable lead standards in Nessler cylinders. RESULTS OF ANALYSEs.-The method of analysis described has been applied to a series of 24-hour specimens of urine collected from hospital patients who for the most part had no history of any industrial exposure to lead.A few of the patients in the series had been employed as plumbers and painters prior to their admission to hospital; they had been removed from abnormal exposure to lead however for periods ranging from 2 to 18 months and showed no symptoms of lead poisoning. The urines from these patients showed no excess of any significance in lead-content compared with the others of the series (see Table I). This indicates that urinary lead examinations are useful in diagnosis only when the exposure to the metal TABLE I ( a ) Urines from Patients with no industrial connection with lead. 17 analyses. Range nil to 0.11 mg. per litre. 0.05 mg. per 24 hours. Urines from patients who had been removed for long periods from their Range nil to 0.14 mg.per litre. Average 0.05 mg. per litre. 0.05 mg. per 24 hours. nil to 0.12 mg. per 24 hours. Average 0-04 mg. per litre. (b) occupational exposure to lead. 8 analyses. nil to 0.11 mg. per 24 hours. Of these 25 specimens 23 contained less than 0-1 mg. of 1ea.d per litre and 22 less than this amount per 24 hours. TABLE I1 RESULTS OF DUPLICATE EXPERIMENTS Vol. of urine analysed ml. 500 700 800 800 500 350 700 700 500 500 375 375 550 750 400 400 Lead found mg. 0.02 0.03 Nil Nil 0.04 0.03 0.01 0.015 Nil 0.01 0.025 0.025 0.04 0.06 0.025 0.025 Lead per litre mg-0.04 0.045 Nil Nil 0.08 0.085 0.015 0-02 Nil 0.02 0.065 0.065 0.075 0.08 0.06 0.0 470 MORTON THE APPLICATION OF DIPHENYL THIOCARBAZONE (DITHIZONE) VOl.of urine ml. 500 500 500 500 600 600 500 500 300 500 500 500 300 600 400 400 400 400 400 400 500 500 500 500 500 500 400 400 400 500 500 500 500 600 600 600 has been recent. TABLE I11 RESULTS OF RECOVERY EXPERIMENTS Lead added mg. None 0.01 0.03 0.05 None 0.05 None 0.08 None 0.10 None 0.10 None 0.20 None 0.20 0.15 0.10 None 0.25 None 0.10 0.20 0.40 None 0.30 None 0.20 0.30 None 0.05 0.15 0.20 None 0.10 0.20 Lead found mg. Nil 0.015 0-035 0.055 0.03 0.08 0.04 0-10 0-005 0.075 0.0 1 0.08 0-005 0.17 0.03 0.20 0.15 0.11 0.025 0.24 0.025 0.11 0.19 0.36 0.025 0.27 0.025 0.19 0.285 0.02 0.07 0.15 0.19 0.035 0.1 10 0.205 Lead recovered mg-0.015 0.035 0.055 0.05 0.06 0.07 0.07 0.165 0.17 0.12 0.08 0.215 0.085 0.165 0.335 0.245 0.165 0-26 0.05 0.13 0.17 0.075 0-17 ----------I I Error -+0-005 +0405 + 0.005 0.00 - 0.02 -0.03 -----0.03 --0.035 --0.03 -0.03 - 0.02 -0.035 ---0.015 -0.035 -0.065 --0.055 1 -0.035 -0.04 0.00 -0.02 -0.03 ---0.025 -0.03 All the results are to the nearest 0.005 mg.In this connection it is of interest to note the possible application of lead-excretion measurements following low calcium with high phosphorus diets, as an aid to diagnosis of lead intoxication (Gray).1° A number of analyses have been duplicated and the results shown in Table 11, indicate the consistency attainable TO T H E ESTIMATION OF LEAD IN URINE 4’71 The results of a number of recovery experiments are given in Table 111.In these experiments known amounts of lead were added as lead acetate to the urines prior to precipitation of the phosphates. Examination of the recorded recovery experiments discloses that there is a loss of lead during the process except when the amount of lead added is small. It also appears that the magnitude of the error increases as the amount of lead to be removed increases. It is very probable that incomplete precipitation of lead with phosphate at the first stage of the procedure and some loss of lead by volatilisa-tion during ashing are the chief factors responsible for these errors.Loss of lead due to its incomplete precipitation with the phosphate has been recorded in the literature and Fairhall has stated that this can be minimised by the use of fresh urine for the analysis. Where urine analyses for lead are to be carried out as part of precise studies of metabolism it would appear advisable to replace phosphate precipitation by a process of wet oxidation. For routine purposes however it usually would be sufficient to employ the less tedious of the two procedures. BIOCHEMICAL DEPARTMENT SELLY OAK HOSPITAL BIRMINGHAM REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. N. L. Allport and G. H. Skrimshire ANALYST 1932 57 440. H. Bohnenkamp and W. Linneweh Arch. Klin. Med. 1933 175 167. T. Cooksey and S. G. Walton ANALYST 1929 54 97. J. Cholak J . Amer. Chem. Soc. 1935 57 104. L. T. Fairhall J . Ind. Hyg. 1922 4 9. - J . Biol. Chem. 1923 57 455. H. Fischer 2. angew. Chem. 1929 42 1025; Mikrochem. 1930 8 319. H. Fischer and G. Leopoldi 2. angew Chem. 1934 47 90. A. G. Francis C. 0. Harvey and J. L. Buchan ANALYST 1929 54 725. I. Gray J . Amer. Med. Ass. 1935 104 200. R. A. Kehoe and F. Thamann id. 1929 92 1418. R. A. Kehoe F. Thamann and J. Cholak J . Ind. Hyg. 1933 15 257. - J . Amer. Med. Ass. 1935 104 90. C. N. Myers F. Gustafson and B. Throne J . Lab. Clin. Med. 1935,20 648. I. M. Rabinowitch A. Dingwall and F. H Mackay J . BioZ. Chem. 1933 103 726

ISSN:0003-2654    

DOI:10.1039/AN9366100465

出版商:RSC    

年代:1936

数据来源: RSC

摘要:

OF MILK: CORRECTION FACTORS AND THE INFLUENCE OF STIRRING: I1 h I11 225 It was originally intended to employ four different amounts of supercooling for each sample of milk, vix. about 1.5, 1.0,0.8, and 0.5" C. It was found, however, that the differences in the readings of the thermometer corresponding to these different amounts of supercooling were in the neighbourhood of 0.002"-an amount so small that the unavoidable errors of observation might possibly approach the same order. It was, therefore, decided to employ only two different amounts of supercooling, as widely apart as practicable, say about 1.5" and 04", and to increase the number of samples examined. It was stated by Hortvet that, unless a much greater amount of supercooling than 0.5" is employed in the use of his cryoscope and technique, the rise of the mercury column is not sufficiently pronounced, and that there is more or less wavering, so that difficulty arises in deciding on the exact point at which the top of the column becomes stationary. Elsdon and Stubbs (Eoc.it.)^ found the same result when using a supercooling of less than about 0.8"; the mercury rose very slowly, and did not maintain a steady position for any appreciable time, and the proper freezing-point might not, under these circumstances, be attained. In the first experiments, made with the object of ascertaining the super- cooling correction, it was observed that where the amount of supercooling was small, that is, less than say 0-75", even in the absence of alcohol in the jacket surrounding the freezing-tube, the rise of temperature, when freezing occurred, was very slow-so slow, indeed, as to suggest doubts whether the thermometer would indicate the freezing-point of the milk, influenced only by supercooling, owing to the reading being affected by the length of time which elapses and the possibility of imperfect thermal insulation, causing a nett loss of heat from the freezing tube and contents.To give an instance; in an experiment when the supercooling was 0-71" the time required for the mercury column to rise until, on observation through the telescope with the aid of the horizontal cross-wire, the ascent became imperceptible, was 92 minutes, as compared with about 3& minutes when the same milk was super- cooled 1-49'. It will be seen later that, in the absence of alcohol in the space surrounding the freezing-tube, the heat insulation of the milk is not perfect; a nett loss of heat occurs, for it is possible t o carry through a freezing-point determination under such conditions.The difference between the two methods of working- with and without alcohol-results in a longer time being required for the cooling of the milk when the space around the freezing-tube is occupied by air. There were also the difficulties of judging when the rising column of mercury had reached the highest point, due to the very slow movement which occurred in that region, and of getting satisfactory readings, owing to the short time that elapsed before a fall took place. The idea of following strictly the Hortvet technique, as regards stirring, for these particular experiments was therefore abandoned.In the first series of experiments, the results of which are recorded in Table 111, four or five stirrings of three strokes each were employed, and in the second series the mechanical stirrer, working at the rate of 40 strokes per minute, was in operation all the time, the thermometer rising until tapping became necessary. It does not appear that these variations in stirring caused any significant differences in the results obtained, but the times of rising of the mercury, after two different extents, large and small,OF MILK: CORRECTION FACTORS AND THE INFLUENCE OF STIRRING: I1 h I11 225 It was originally intended to employ four different amounts of supercooling for each sample of milk, vix.about 1.5, 1.0,0.8, and 0.5" C. It was found, however, that the differences in the readings of the thermometer corresponding to these different amounts of supercooling were in the neighbourhood of 0.002"-an amount so small that the unavoidable errors of observation might possibly approach the same order. It was, therefore, decided to employ only two different amounts of supercooling, as widely apart as practicable, say about 1.5" and 04", and to increase the number of samples examined. It was stated by Hortvet that, unless a much greater amount of supercooling than 0.5" is employed in the use of his cryoscope and technique, the rise of the mercury column is not sufficiently pronounced, and that there is more or less wavering, so that difficulty arises in deciding on the exact point at which the top of the column becomes stationary.Elsdon and Stubbs (Eoc. it.)^ found the same result when using a supercooling of less than about 0.8"; the mercury rose very slowly, and did not maintain a steady position for any appreciable time, and the proper freezing-point might not, under these circumstances, be attained. In the first experiments, made with the object of ascertaining the super- cooling correction, it was observed that where the amount of supercooling was small, that is, less than say 0-75", even in the absence of alcohol in the jacket surrounding the freezing-tube, the rise of temperature, when freezing occurred, was very slow-so slow, indeed, as to suggest doubts whether the thermometer would indicate the freezing-point of the milk, influenced only by supercooling, owing to the reading being affected by the length of time which elapses and the possibility of imperfect thermal insulation, causing a nett loss of heat from the freezing tube and contents.To give an instance; in an experiment when the supercooling was 0-71" the time required for the mercury column to rise until, on observation through the telescope with the aid of the horizontal cross-wire, the ascent became imperceptible, was 92 minutes, as compared with about 3& minutes when the same milk was super- cooled 1-49'. It will be seen later that, in the absence of alcohol in the space surrounding the freezing-tube, the heat insulation of the milk is not perfect; a nett loss of heat occurs, for it is possible t o carry through a freezing-point determination under such conditions.The difference between the two methods of working- with and without alcohol-results in a longer time being required for the cooling of the milk when the space around the freezing-tube is occupied by air. There were also the difficulties of judging when the rising column of mercury had reached the highest point, due to the very slow movement which occurred in that region, and of getting satisfactory readings, owing to the short time that elapsed before a fall took place. The idea of following strictly the Hortvet technique, as regards stirring, for these particular experiments was therefore abandoned. In the first series of experiments, the results of which are recorded in Table 111, four or five stirrings of three strokes each were employed, and in the second series the mechanical stirrer, working at the rate of 40 strokes per minute, was in operation all the time, the thermometer rising until tapping became necessary. It does not appear that these variations in stirring caused any significant differences in the results obtained, but the times of rising of the mercury, after two different extents, large and small,

ISSN:0003-2654    

DOI:10.1039/AN9366100472

出版商:RSC    

年代:1936

数据来源: RSC

摘要:

OF MILK: CORRECTION FACTORS AND THE INFLUENCE OF STIRRING: I1 h I11 225 It was originally intended to employ four different amounts of supercooling for each sample of milk, vix. about 1.5, 1.0,0.8, and 0.5" C. It was found, however, that the differences in the readings of the thermometer corresponding to these different amounts of supercooling were in the neighbourhood of 0.002"-an amount so small that the unavoidable errors of observation might possibly approach the same order. It was, therefore, decided to employ only two different amounts of supercooling, as widely apart as practicable, say about 1.5" and 04", and to increase the number of samples examined. It was stated by Hortvet that, unless a much greater amount of supercooling than 0.5" is employed in the use of his cryoscope and technique, the rise of the mercury column is not sufficiently pronounced, and that there is more or less wavering, so that difficulty arises in deciding on the exact point at which the top of the column becomes stationary. Elsdon and Stubbs (Eoc.it.)^ found the same result when using a supercooling of less than about 0.8"; the mercury rose very slowly, and did not maintain a steady position for any appreciable time, and the proper freezing-point might not, under these circumstances, be attained. In the first experiments, made with the object of ascertaining the super- cooling correction, it was observed that where the amount of supercooling was small, that is, less than say 0-75", even in the absence of alcohol in the jacket surrounding the freezing-tube, the rise of temperature, when freezing occurred, was very slow-so slow, indeed, as to suggest doubts whether the thermometer would indicate the freezing-point of the milk, influenced only by supercooling, owing to the reading being affected by the length of time which elapses and the possibility of imperfect thermal insulation, causing a nett loss of heat from the freezing tube and contents.To give an instance; in an experiment when the supercooling was 0-71" the time required for the mercury column to rise until, on observation through the telescope with the aid of the horizontal cross-wire, the ascent became imperceptible, was 92 minutes, as compared with about 3& minutes when the same milk was super- cooled 1-49'. It will be seen later that, in the absence of alcohol in the space surrounding the freezing-tube, the heat insulation of the milk is not perfect; a nett loss of heat occurs, for it is possible t o carry through a freezing-point determination under such conditions.The difference between the two methods of working- with and without alcohol-results in a longer time being required for the cooling of the milk when the space around the freezing-tube is occupied by air. There were also the difficulties of judging when the rising column of mercury had reached the highest point, due to the very slow movement which occurred in that region, and of getting satisfactory readings, owing to the short time that elapsed before a fall took place. The idea of following strictly the Hortvet technique, as regards stirring, for these particular experiments was therefore abandoned.In the first series of experiments, the results of which are recorded in Table 111, four or five stirrings of three strokes each were employed, and in the second series the mechanical stirrer, working at the rate of 40 strokes per minute, was in operation all the time, the thermometer rising until tapping became necessary. It does not appear that these variations in stirring caused any significant differences in the results obtained, but the times of rising of the mercury, after two different extents, large and small,OF MILK: CORRECTION FACTORS AND THE INFLUENCE OF STIRRING: I1 h I11 225 It was originally intended to employ four different amounts of supercooling for each sample of milk, vix.about 1.5, 1.0,0.8, and 0.5" C. It was found, however, that the differences in the readings of the thermometer corresponding to these different amounts of supercooling were in the neighbourhood of 0.002"-an amount so small that the unavoidable errors of observation might possibly approach the same order. It was, therefore, decided to employ only two different amounts of supercooling, as widely apart as practicable, say about 1.5" and 04", and to increase the number of samples examined. It was stated by Hortvet that, unless a much greater amount of supercooling than 0.5" is employed in the use of his cryoscope and technique, the rise of the mercury column is not sufficiently pronounced, and that there is more or less wavering, so that difficulty arises in deciding on the exact point at which the top of the column becomes stationary.Elsdon and Stubbs (Eoc. it.)^ found the same result when using a supercooling of less than about 0.8"; the mercury rose very slowly, and did not maintain a steady position for any appreciable time, and the proper freezing-point might not, under these circumstances, be attained. In the first experiments, made with the object of ascertaining the super- cooling correction, it was observed that where the amount of supercooling was small, that is, less than say 0-75", even in the absence of alcohol in the jacket surrounding the freezing-tube, the rise of temperature, when freezing occurred, was very slow-so slow, indeed, as to suggest doubts whether the thermometer would indicate the freezing-point of the milk, influenced only by supercooling, owing to the reading being affected by the length of time which elapses and the possibility of imperfect thermal insulation, causing a nett loss of heat from the freezing tube and contents.To give an instance; in an experiment when the supercooling was 0-71" the time required for the mercury column to rise until, on observation through the telescope with the aid of the horizontal cross-wire, the ascent became imperceptible, was 92 minutes, as compared with about 3& minutes when the same milk was super- cooled 1-49'. It will be seen later that, in the absence of alcohol in the space surrounding the freezing-tube, the heat insulation of the milk is not perfect; a nett loss of heat occurs, for it is possible t o carry through a freezing-point determination under such conditions.The difference between the two methods of working- with and without alcohol-results in a longer time being required for the cooling of the milk when the space around the freezing-tube is occupied by air. There were also the difficulties of judging when the rising column of mercury had reached the highest point, due to the very slow movement which occurred in that region, and of getting satisfactory readings, owing to the short time that elapsed before a fall took place. The idea of following strictly the Hortvet technique, as regards stirring, for these particular experiments was therefore abandoned. In the first series of experiments, the results of which are recorded in Table 111, four or five stirrings of three strokes each were employed, and in the second series the mechanical stirrer, working at the rate of 40 strokes per minute, was in operation all the time, the thermometer rising until tapping became necessary. It does not appear that these variations in stirring caused any significant differences in the results obtained, but the times of rising of the mercury, after two different extents, large and small,

ISSN:0003-2654    

DOI:10.1039/AN936610474b

出版商:RSC    

年代:1936

数据来源: RSC

摘要:

OF MILK: CORRECTION FACTORS AND THE INFLUENCE OF STIRRING: I1 h I11 225 It was originally intended to employ four different amounts of supercooling for each sample of milk, vix. about 1.5, 1.0,0.8, and 0.5" C. It was found, however, that the differences in the readings of the thermometer corresponding to these different amounts of supercooling were in the neighbourhood of 0.002"-an amount so small that the unavoidable errors of observation might possibly approach the same order. It was, therefore, decided to employ only two different amounts of supercooling, as widely apart as practicable, say about 1.5" and 04", and to increase the number of samples examined. It was stated by Hortvet that, unless a much greater amount of supercooling than 0.5" is employed in the use of his cryoscope and technique, the rise of the mercury column is not sufficiently pronounced, and that there is more or less wavering, so that difficulty arises in deciding on the exact point at which the top of the column becomes stationary. Elsdon and Stubbs (Eoc.it.)^ found the same result when using a supercooling of less than about 0.8"; the mercury rose very slowly, and did not maintain a steady position for any appreciable time, and the proper freezing-point might not, under these circumstances, be attained. In the first experiments, made with the object of ascertaining the super- cooling correction, it was observed that where the amount of supercooling was small, that is, less than say 0-75", even in the absence of alcohol in the jacket surrounding the freezing-tube, the rise of temperature, when freezing occurred, was very slow-so slow, indeed, as to suggest doubts whether the thermometer would indicate the freezing-point of the milk, influenced only by supercooling, owing to the reading being affected by the length of time which elapses and the possibility of imperfect thermal insulation, causing a nett loss of heat from the freezing tube and contents.To give an instance; in an experiment when the supercooling was 0-71" the time required for the mercury column to rise until, on observation through the telescope with the aid of the horizontal cross-wire, the ascent became imperceptible, was 92 minutes, as compared with about 3& minutes when the same milk was super- cooled 1-49'. It will be seen later that, in the absence of alcohol in the space surrounding the freezing-tube, the heat insulation of the milk is not perfect; a nett loss of heat occurs, for it is possible t o carry through a freezing-point determination under such conditions.The difference between the two methods of working- with and without alcohol-results in a longer time being required for the cooling of the milk when the space around the freezing-tube is occupied by air. There were also the difficulties of judging when the rising column of mercury had reached the highest point, due to the very slow movement which occurred in that region, and of getting satisfactory readings, owing to the short time that elapsed before a fall took place. The idea of following strictly the Hortvet technique, as regards stirring, for these particular experiments was therefore abandoned.In the first series of experiments, the results of which are recorded in Table 111, four or five stirrings of three strokes each were employed, and in the second series the mechanical stirrer, working at the rate of 40 strokes per minute, was in operation all the time, the thermometer rising until tapping became necessary. It does not appear that these variations in stirring caused any significant differences in the results obtained, but the times of rising of the mercury, after two different extents, large and small,OF MILK: CORRECTION FACTORS AND THE INFLUENCE OF STIRRING: I1 h I11 225 It was originally intended to employ four different amounts of supercooling for each sample of milk, vix.about 1.5, 1.0,0.8, and 0.5" C. It was found, however, that the differences in the readings of the thermometer corresponding to these different amounts of supercooling were in the neighbourhood of 0.002"-an amount so small that the unavoidable errors of observation might possibly approach the same order. It was, therefore, decided to employ only two different amounts of supercooling, as widely apart as practicable, say about 1.5" and 04", and to increase the number of samples examined. It was stated by Hortvet that, unless a much greater amount of supercooling than 0.5" is employed in the use of his cryoscope and technique, the rise of the mercury column is not sufficiently pronounced, and that there is more or less wavering, so that difficulty arises in deciding on the exact point at which the top of the column becomes stationary.Elsdon and Stubbs (Eoc. it.)^ found the same result when using a supercooling of less than about 0.8"; the mercury rose very slowly, and did not maintain a steady position for any appreciable time, and the proper freezing-point might not, under these circumstances, be attained. In the first experiments, made with the object of ascertaining the super- cooling correction, it was observed that where the amount of supercooling was small, that is, less than say 0-75", even in the absence of alcohol in the jacket surrounding the freezing-tube, the rise of temperature, when freezing occurred, was very slow-so slow, indeed, as to suggest doubts whether the thermometer would indicate the freezing-point of the milk, influenced only by supercooling, owing to the reading being affected by the length of time which elapses and the possibility of imperfect thermal insulation, causing a nett loss of heat from the freezing tube and contents.To give an instance; in an experiment when the supercooling was 0-71" the time required for the mercury column to rise until, on observation through the telescope with the aid of the horizontal cross-wire, the ascent became imperceptible, was 92 minutes, as compared with about 3& minutes when the same milk was super- cooled 1-49'. It will be seen later that, in the absence of alcohol in the space surrounding the freezing-tube, the heat insulation of the milk is not perfect; a nett loss of heat occurs, for it is possible t o carry through a freezing-point determination under such conditions.The difference between the two methods of working- with and without alcohol-results in a longer time being required for the cooling of the milk when the space around the freezing-tube is occupied by air. There were also the difficulties of judging when the rising column of mercury had reached the highest point, due to the very slow movement which occurred in that region, and of getting satisfactory readings, owing to the short time that elapsed before a fall took place. The idea of following strictly the Hortvet technique, as regards stirring, for these particular experiments was therefore abandoned. In the first series of experiments, the results of which are recorded in Table 111, four or five stirrings of three strokes each were employed, and in the second series the mechanical stirrer, working at the rate of 40 strokes per minute, was in operation all the time, the thermometer rising until tapping became necessary.It does not appear that these variations in stirring caused any significant differences in the results obtained, but the times of rising of the mercury, after two different extents, large and small,OF MILK: CORRECTION FACTORS AND THE INFLUENCE OF STIRRING: I1 h I11 225 It was originally intended to employ four different amounts of supercooling for each sample of milk, vix. about 1.5, 1.0,0.8, and 0.5" C. It was found, however, that the differences in the readings of the thermometer corresponding to these different amounts of supercooling were in the neighbourhood of 0.002"-an amount so small that the unavoidable errors of observation might possibly approach the same order.It was, therefore, decided to employ only two different amounts of supercooling, as widely apart as practicable, say about 1.5" and 04", and to increase the number of samples examined. It was stated by Hortvet that, unless a much greater amount of supercooling than 0.5" is employed in the use of his cryoscope and technique, the rise of the mercury column is not sufficiently pronounced, and that there is more or less wavering, so that difficulty arises in deciding on the exact point at which the top of the column becomes stationary. Elsdon and Stubbs (Eoc. it.)^ found the same result when using a supercooling of less than about 0.8"; the mercury rose very slowly, and did not maintain a steady position for any appreciable time, and the proper freezing-point might not, under these circumstances, be attained.In the first experiments, made with the object of ascertaining the super- cooling correction, it was observed that where the amount of supercooling was small, that is, less than say 0-75", even in the absence of alcohol in the jacket surrounding the freezing-tube, the rise of temperature, when freezing occurred, was very slow-so slow, indeed, as to suggest doubts whether the thermometer would indicate the freezing-point of the milk, influenced only by supercooling, owing to the reading being affected by the length of time which elapses and the possibility of imperfect thermal insulation, causing a nett loss of heat from the freezing tube and contents. To give an instance; in an experiment when the supercooling was 0-71" the time required for the mercury column to rise until, on observation through the telescope with the aid of the horizontal cross-wire, the ascent became imperceptible, was 92 minutes, as compared with about 3& minutes when the same milk was super- cooled 1-49'.It will be seen later that, in the absence of alcohol in the space surrounding the freezing-tube, the heat insulation of the milk is not perfect; a nett loss of heat occurs, for it is possible t o carry through a freezing-point determination under such conditions. The difference between the two methods of working- with and without alcohol-results in a longer time being required for the cooling of the milk when the space around the freezing-tube is occupied by air.There were also the difficulties of judging when the rising column of mercury had reached the highest point, due to the very slow movement which occurred in that region, and of getting satisfactory readings, owing to the short time that elapsed before a fall took place. The idea of following strictly the Hortvet technique, as regards stirring, for these particular experiments was therefore abandoned. In the first series of experiments, the results of which are recorded in Table 111, four or five stirrings of three strokes each were employed, and in the second series the mechanical stirrer, working at the rate of 40 strokes per minute, was in operation all the time, the thermometer rising until tapping became necessary.It does not appear that these variations in stirring caused any significant differences in the results obtained, but the times of rising of the mercury, after two different extents, large and small,OF MILK: CORRECTION FACTORS AND THE INFLUENCE OF STIRRING: I1 h I11 225 It was originally intended to employ four different amounts of supercooling for each sample of milk, vix. about 1.5, 1.0,0.8, and 0.5" C. It was found, however, that the differences in the readings of the thermometer corresponding to these different amounts of supercooling were in the neighbourhood of 0.002"-an amount so small that the unavoidable errors of observation might possibly approach the same order. It was, therefore, decided to employ only two different amounts of supercooling, as widely apart as practicable, say about 1.5" and 04", and to increase the number of samples examined.It was stated by Hortvet that, unless a much greater amount of supercooling than 0.5" is employed in the use of his cryoscope and technique, the rise of the mercury column is not sufficiently pronounced, and that there is more or less wavering, so that difficulty arises in deciding on the exact point at which the top of the column becomes stationary. Elsdon and Stubbs (Eoc. it.)^ found the same result when using a supercooling of less than about 0.8"; the mercury rose very slowly, and did not maintain a steady position for any appreciable time, and the proper freezing-point might not, under these circumstances, be attained. In the first experiments, made with the object of ascertaining the super- cooling correction, it was observed that where the amount of supercooling was small, that is, less than say 0-75", even in the absence of alcohol in the jacket surrounding the freezing-tube, the rise of temperature, when freezing occurred, was very slow-so slow, indeed, as to suggest doubts whether the thermometer would indicate the freezing-point of the milk, influenced only by supercooling, owing to the reading being affected by the length of time which elapses and the possibility of imperfect thermal insulation, causing a nett loss of heat from the freezing tube and contents.To give an instance; in an experiment when the supercooling was 0-71" the time required for the mercury column to rise until, on observation through the telescope with the aid of the horizontal cross-wire, the ascent became imperceptible, was 92 minutes, as compared with about 3& minutes when the same milk was super- cooled 1-49'.It will be seen later that, in the absence of alcohol in the space surrounding the freezing-tube, the heat insulation of the milk is not perfect; a nett loss of heat occurs, for it is possible t o carry through a freezing-point determination under such conditions. The difference between the two methods of working- with and without alcohol-results in a longer time being required for the cooling of the milk when the space around the freezing-tube is occupied by air. There were also the difficulties of judging when the rising column of mercury had reached the highest point, due to the very slow movement which occurred in that region, and of getting satisfactory readings, owing to the short time that elapsed before a fall took place. The idea of following strictly the Hortvet technique, as regards stirring, for these particular experiments was therefore abandoned. In the first series of experiments, the results of which are recorded in Table 111, four or five stirrings of three strokes each were employed, and in the second series the mechanical stirrer, working at the rate of 40 strokes per minute, was in operation all the time, the thermometer rising until tapping became necessary. It does not appear that these variations in stirring caused any significant differences in the results obtained, but the times of rising of the mercury, after two different extents, large and small,

ISSN:0003-2654    

DOI:10.1039/AN9366100475

出版商:RSC    

年代:1936

数据来源: RSC

摘要:

OF MILK: CORRECTION FACTORS AND THE INFLUENCE OF STIRRING: I1 h I11 225 It was originally intended to employ four different amounts of supercooling for each sample of milk, vix. about 1.5, 1.0,0.8, and 0.5" C. It was found, however, that the differences in the readings of the thermometer corresponding to these different amounts of supercooling were in the neighbourhood of 0.002"-an amount so small that the unavoidable errors of observation might possibly approach the same order. It was, therefore, decided to employ only two different amounts of supercooling, as widely apart as practicable, say about 1.5" and 04", and to increase the number of samples examined. It was stated by Hortvet that, unless a much greater amount of supercooling than 0.5" is employed in the use of his cryoscope and technique, the rise of the mercury column is not sufficiently pronounced, and that there is more or less wavering, so that difficulty arises in deciding on the exact point at which the top of the column becomes stationary. Elsdon and Stubbs (Eoc.it.)^ found the same result when using a supercooling of less than about 0.8"; the mercury rose very slowly, and did not maintain a steady position for any appreciable time, and the proper freezing-point might not, under these circumstances, be attained. In the first experiments, made with the object of ascertaining the super- cooling correction, it was observed that where the amount of supercooling was small, that is, less than say 0-75", even in the absence of alcohol in the jacket surrounding the freezing-tube, the rise of temperature, when freezing occurred, was very slow-so slow, indeed, as to suggest doubts whether the thermometer would indicate the freezing-point of the milk, influenced only by supercooling, owing to the reading being affected by the length of time which elapses and the possibility of imperfect thermal insulation, causing a nett loss of heat from the freezing tube and contents.To give an instance; in an experiment when the supercooling was 0-71" the time required for the mercury column to rise until, on observation through the telescope with the aid of the horizontal cross-wire, the ascent became imperceptible, was 92 minutes, as compared with about 3& minutes when the same milk was super- cooled 1-49'. It will be seen later that, in the absence of alcohol in the space surrounding the freezing-tube, the heat insulation of the milk is not perfect; a nett loss of heat occurs, for it is possible t o carry through a freezing-point determination under such conditions.The difference between the two methods of working- with and without alcohol-results in a longer time being required for the cooling of the milk when the space around the freezing-tube is occupied by air. There were also the difficulties of judging when the rising column of mercury had reached the highest point, due to the very slow movement which occurred in that region, and of getting satisfactory readings, owing to the short time that elapsed before a fall took place. The idea of following strictly the Hortvet technique, as regards stirring, for these particular experiments was therefore abandoned.In the first series of experiments, the results of which are recorded in Table 111, four or five stirrings of three strokes each were employed, and in the second series the mechanical stirrer, working at the rate of 40 strokes per minute, was in operation all the time, the thermometer rising until tapping became necessary. It does not appear that these variations in stirring caused any significant differences in the results obtained, but the times of rising of the mercury, after two different extents, large and small,OF MILK: CORRECTION FACTORS AND THE INFLUENCE OF STIRRING: I1 h I11 225 It was originally intended to employ four different amounts of supercooling for each sample of milk, vix.about 1.5, 1.0,0.8, and 0.5" C. It was found, however, that the differences in the readings of the thermometer corresponding to these different amounts of supercooling were in the neighbourhood of 0.002"-an amount so small that the unavoidable errors of observation might possibly approach the same order. It was, therefore, decided to employ only two different amounts of supercooling, as widely apart as practicable, say about 1.5" and 04", and to increase the number of samples examined. It was stated by Hortvet that, unless a much greater amount of supercooling than 0.5" is employed in the use of his cryoscope and technique, the rise of the mercury column is not sufficiently pronounced, and that there is more or less wavering, so that difficulty arises in deciding on the exact point at which the top of the column becomes stationary.Elsdon and Stubbs (Eoc. it.)^ found the same result when using a supercooling of less than about 0.8"; the mercury rose very slowly, and did not maintain a steady position for any appreciable time, and the proper freezing-point might not, under these circumstances, be attained. In the first experiments, made with the object of ascertaining the super- cooling correction, it was observed that where the amount of supercooling was small, that is, less than say 0-75", even in the absence of alcohol in the jacket surrounding the freezing-tube, the rise of temperature, when freezing occurred, was very slow-so slow, indeed, as to suggest doubts whether the thermometer would indicate the freezing-point of the milk, influenced only by supercooling, owing to the reading being affected by the length of time which elapses and the possibility of imperfect thermal insulation, causing a nett loss of heat from the freezing tube and contents.To give an instance; in an experiment when the supercooling was 0-71" the time required for the mercury column to rise until, on observation through the telescope with the aid of the horizontal cross-wire, the ascent became imperceptible, was 92 minutes, as compared with about 3& minutes when the same milk was super- cooled 1-49'. It will be seen later that, in the absence of alcohol in the space surrounding the freezing-tube, the heat insulation of the milk is not perfect; a nett loss of heat occurs, for it is possible t o carry through a freezing-point determination under such conditions.The difference between the two methods of working- with and without alcohol-results in a longer time being required for the cooling of the milk when the space around the freezing-tube is occupied by air. There were also the difficulties of judging when the rising column of mercury had reached the highest point, due to the very slow movement which occurred in that region, and of getting satisfactory readings, owing to the short time that elapsed before a fall took place. The idea of following strictly the Hortvet technique, as regards stirring, for these particular experiments was therefore abandoned. In the first series of experiments, the results of which are recorded in Table 111, four or five stirrings of three strokes each were employed, and in the second series the mechanical stirrer, working at the rate of 40 strokes per minute, was in operation all the time, the thermometer rising until tapping became necessary.It does not appear that these variations in stirring caused any significant differences in the results obtained, but the times of rising of the mercury, after two different extents, large and small,OF MILK: CORRECTION FACTORS AND THE INFLUENCE OF STIRRING: I1 h I11 225 It was originally intended to employ four different amounts of supercooling for each sample of milk, vix. about 1.5, 1.0,0.8, and 0.5" C. It was found, however, that the differences in the readings of the thermometer corresponding to these different amounts of supercooling were in the neighbourhood of 0.002"-an amount so small that the unavoidable errors of observation might possibly approach the same order.It was, therefore, decided to employ only two different amounts of supercooling, as widely apart as practicable, say about 1.5" and 04", and to increase the number of samples examined. It was stated by Hortvet that, unless a much greater amount of supercooling than 0.5" is employed in the use of his cryoscope and technique, the rise of the mercury column is not sufficiently pronounced, and that there is more or less wavering, so that difficulty arises in deciding on the exact point at which the top of the column becomes stationary. Elsdon and Stubbs (Eoc. it.)^ found the same result when using a supercooling of less than about 0.8"; the mercury rose very slowly, and did not maintain a steady position for any appreciable time, and the proper freezing-point might not, under these circumstances, be attained.In the first experiments, made with the object of ascertaining the super- cooling correction, it was observed that where the amount of supercooling was small, that is, less than say 0-75", even in the absence of alcohol in the jacket surrounding the freezing-tube, the rise of temperature, when freezing occurred, was very slow-so slow, indeed, as to suggest doubts whether the thermometer would indicate the freezing-point of the milk, influenced only by supercooling, owing to the reading being affected by the length of time which elapses and the possibility of imperfect thermal insulation, causing a nett loss of heat from the freezing tube and contents. To give an instance; in an experiment when the supercooling was 0-71" the time required for the mercury column to rise until, on observation through the telescope with the aid of the horizontal cross-wire, the ascent became imperceptible, was 92 minutes, as compared with about 3& minutes when the same milk was super- cooled 1-49'.It will be seen later that, in the absence of alcohol in the space surrounding the freezing-tube, the heat insulation of the milk is not perfect; a nett loss of heat occurs, for it is possible t o carry through a freezing-point determination under such conditions. The difference between the two methods of working- with and without alcohol-results in a longer time being required for the cooling of the milk when the space around the freezing-tube is occupied by air.There were also the difficulties of judging when the rising column of mercury had reached the highest point, due to the very slow movement which occurred in that region, and of getting satisfactory readings, owing to the short time that elapsed before a fall took place. The idea of following strictly the Hortvet technique, as regards stirring, for these particular experiments was therefore abandoned. In the first series of experiments, the results of which are recorded in Table 111, four or five stirrings of three strokes each were employed, and in the second series the mechanical stirrer, working at the rate of 40 strokes per minute, was in operation all the time, the thermometer rising until tapping became necessary.It does not appear that these variations in stirring caused any significant differences in the results obtained, but the times of rising of the mercury, after two different extents, large and small,OF MILK: CORRECTION FACTORS AND THE INFLUENCE OF STIRRING: I1 h I11 225 It was originally intended to employ four different amounts of supercooling for each sample of milk, vix. about 1.5, 1.0,0.8, and 0.5" C. It was found, however, that the differences in the readings of the thermometer corresponding to these different amounts of supercooling were in the neighbourhood of 0.002"-an amount so small that the unavoidable errors of observation might possibly approach the same order. It was, therefore, decided to employ only two different amounts of supercooling, as widely apart as practicable, say about 1.5" and 04", and to increase the number of samples examined.It was stated by Hortvet that, unless a much greater amount of supercooling than 0.5" is employed in the use of his cryoscope and technique, the rise of the mercury column is not sufficiently pronounced, and that there is more or less wavering, so that difficulty arises in deciding on the exact point at which the top of the column becomes stationary. Elsdon and Stubbs (Eoc. it.)^ found the same result when using a supercooling of less than about 0.8"; the mercury rose very slowly, and did not maintain a steady position for any appreciable time, and the proper freezing-point might not, under these circumstances, be attained. In the first experiments, made with the object of ascertaining the super- cooling correction, it was observed that where the amount of supercooling was small, that is, less than say 0-75", even in the absence of alcohol in the jacket surrounding the freezing-tube, the rise of temperature, when freezing occurred, was very slow-so slow, indeed, as to suggest doubts whether the thermometer would indicate the freezing-point of the milk, influenced only by supercooling, owing to the reading being affected by the length of time which elapses and the possibility of imperfect thermal insulation, causing a nett loss of heat from the freezing tube and contents.To give an instance; in an experiment when the supercooling was 0-71" the time required for the mercury column to rise until, on observation through the telescope with the aid of the horizontal cross-wire, the ascent became imperceptible, was 92 minutes, as compared with about 3& minutes when the same milk was super- cooled 1-49'.It will be seen later that, in the absence of alcohol in the space surrounding the freezing-tube, the heat insulation of the milk is not perfect; a nett loss of heat occurs, for it is possible t o carry through a freezing-point determination under such conditions. The difference between the two methods of working- with and without alcohol-results in a longer time being required for the cooling of the milk when the space around the freezing-tube is occupied by air. There were also the difficulties of judging when the rising column of mercury had reached the highest point, due to the very slow movement which occurred in that region, and of getting satisfactory readings, owing to the short time that elapsed before a fall took place. The idea of following strictly the Hortvet technique, as regards stirring, for these particular experiments was therefore abandoned. In the first series of experiments, the results of which are recorded in Table 111, four or five stirrings of three strokes each were employed, and in the second series the mechanical stirrer, working at the rate of 40 strokes per minute, was in operation all the time, the thermometer rising until tapping became necessary. It does not appear that these variations in stirring caused any significant differences in the results obtained, but the times of rising of the mercury, after two different extents, large and small,

ISSN:0003-2654    

DOI:10.1039/AN9366100478

出版商:RSC    

年代:1936

数据来源: RSC

摘要:

OF MILK: CORRECTION FACTORS AND THE INFLUENCE OF STIRRING: I1 h I11 225 It was originally intended to employ four different amounts of supercooling for each sample of milk, vix. about 1.5, 1.0,0.8, and 0.5" C. It was found, however, that the differences in the readings of the thermometer corresponding to these different amounts of supercooling were in the neighbourhood of 0.002"-an amount so small that the unavoidable errors of observation might possibly approach the same order. It was, therefore, decided to employ only two different amounts of supercooling, as widely apart as practicable, say about 1.5" and 04", and to increase the number of samples examined. It was stated by Hortvet that, unless a much greater amount of supercooling than 0.5" is employed in the use of his cryoscope and technique, the rise of the mercury column is not sufficiently pronounced, and that there is more or less wavering, so that difficulty arises in deciding on the exact point at which the top of the column becomes stationary. Elsdon and Stubbs (Eoc.it.)^ found the same result when using a supercooling of less than about 0.8"; the mercury rose very slowly, and did not maintain a steady position for any appreciable time, and the proper freezing-point might not, under these circumstances, be attained. In the first experiments, made with the object of ascertaining the super- cooling correction, it was observed that where the amount of supercooling was small, that is, less than say 0-75", even in the absence of alcohol in the jacket surrounding the freezing-tube, the rise of temperature, when freezing occurred, was very slow-so slow, indeed, as to suggest doubts whether the thermometer would indicate the freezing-point of the milk, influenced only by supercooling, owing to the reading being affected by the length of time which elapses and the possibility of imperfect thermal insulation, causing a nett loss of heat from the freezing tube and contents.To give an instance; in an experiment when the supercooling was 0-71" the time required for the mercury column to rise until, on observation through the telescope with the aid of the horizontal cross-wire, the ascent became imperceptible, was 92 minutes, as compared with about 3& minutes when the same milk was super- cooled 1-49'. It will be seen later that, in the absence of alcohol in the space surrounding the freezing-tube, the heat insulation of the milk is not perfect; a nett loss of heat occurs, for it is possible t o carry through a freezing-point determination under such conditions.The difference between the two methods of working- with and without alcohol-results in a longer time being required for the cooling of the milk when the space around the freezing-tube is occupied by air. There were also the difficulties of judging when the rising column of mercury had reached the highest point, due to the very slow movement which occurred in that region, and of getting satisfactory readings, owing to the short time that elapsed before a fall took place. The idea of following strictly the Hortvet technique, as regards stirring, for these particular experiments was therefore abandoned.In the first series of experiments, the results of which are recorded in Table 111, four or five stirrings of three strokes each were employed, and in the second series the mechanical stirrer, working at the rate of 40 strokes per minute, was in operation all the time, the thermometer rising until tapping became necessary. It does not appear that these variations in stirring caused any significant differences in the results obtained, but the times of rising of the mercury, after two different extents, large and small,OF MILK: CORRECTION FACTORS AND THE INFLUENCE OF STIRRING: I1 h I11 225 It was originally intended to employ four different amounts of supercooling for each sample of milk, vix.about 1.5, 1.0,0.8, and 0.5" C. It was found, however, that the differences in the readings of the thermometer corresponding to these different amounts of supercooling were in the neighbourhood of 0.002"-an amount so small that the unavoidable errors of observation might possibly approach the same order. It was, therefore, decided to employ only two different amounts of supercooling, as widely apart as practicable, say about 1.5" and 04", and to increase the number of samples examined. It was stated by Hortvet that, unless a much greater amount of supercooling than 0.5" is employed in the use of his cryoscope and technique, the rise of the mercury column is not sufficiently pronounced, and that there is more or less wavering, so that difficulty arises in deciding on the exact point at which the top of the column becomes stationary.Elsdon and Stubbs (Eoc. it.)^ found the same result when using a supercooling of less than about 0.8"; the mercury rose very slowly, and did not maintain a steady position for any appreciable time, and the proper freezing-point might not, under these circumstances, be attained. In the first experiments, made with the object of ascertaining the super- cooling correction, it was observed that where the amount of supercooling was small, that is, less than say 0-75", even in the absence of alcohol in the jacket surrounding the freezing-tube, the rise of temperature, when freezing occurred, was very slow-so slow, indeed, as to suggest doubts whether the thermometer would indicate the freezing-point of the milk, influenced only by supercooling, owing to the reading being affected by the length of time which elapses and the possibility of imperfect thermal insulation, causing a nett loss of heat from the freezing tube and contents.To give an instance; in an experiment when the supercooling was 0-71" the time required for the mercury column to rise until, on observation through the telescope with the aid of the horizontal cross-wire, the ascent became imperceptible, was 92 minutes, as compared with about 3& minutes when the same milk was super- cooled 1-49'. It will be seen later that, in the absence of alcohol in the space surrounding the freezing-tube, the heat insulation of the milk is not perfect; a nett loss of heat occurs, for it is possible t o carry through a freezing-point determination under such conditions.The difference between the two methods of working- with and without alcohol-results in a longer time being required for the cooling of the milk when the space around the freezing-tube is occupied by air. There were also the difficulties of judging when the rising column of mercury had reached the highest point, due to the very slow movement which occurred in that region, and of getting satisfactory readings, owing to the short time that elapsed before a fall took place. The idea of following strictly the Hortvet technique, as regards stirring, for these particular experiments was therefore abandoned. In the first series of experiments, the results of which are recorded in Table 111, four or five stirrings of three strokes each were employed, and in the second series the mechanical stirrer, working at the rate of 40 strokes per minute, was in operation all the time, the thermometer rising until tapping became necessary.It does not appear that these variations in stirring caused any significant differences in the results obtained, but the times of rising of the mercury, after two different extents, large and small,OF MILK: CORRECTION FACTORS AND THE INFLUENCE OF STIRRING: I1 h I11 225 It was originally intended to employ four different amounts of supercooling for each sample of milk, vix. about 1.5, 1.0,0.8, and 0.5" C. It was found, however, that the differences in the readings of the thermometer corresponding to these different amounts of supercooling were in the neighbourhood of 0.002"-an amount so small that the unavoidable errors of observation might possibly approach the same order.It was, therefore, decided to employ only two different amounts of supercooling, as widely apart as practicable, say about 1.5" and 04", and to increase the number of samples examined. It was stated by Hortvet that, unless a much greater amount of supercooling than 0.5" is employed in the use of his cryoscope and technique, the rise of the mercury column is not sufficiently pronounced, and that there is more or less wavering, so that difficulty arises in deciding on the exact point at which the top of the column becomes stationary. Elsdon and Stubbs (Eoc. it.)^ found the same result when using a supercooling of less than about 0.8"; the mercury rose very slowly, and did not maintain a steady position for any appreciable time, and the proper freezing-point might not, under these circumstances, be attained.In the first experiments, made with the object of ascertaining the super- cooling correction, it was observed that where the amount of supercooling was small, that is, less than say 0-75", even in the absence of alcohol in the jacket surrounding the freezing-tube, the rise of temperature, when freezing occurred, was very slow-so slow, indeed, as to suggest doubts whether the thermometer would indicate the freezing-point of the milk, influenced only by supercooling, owing to the reading being affected by the length of time which elapses and the possibility of imperfect thermal insulation, causing a nett loss of heat from the freezing tube and contents. To give an instance; in an experiment when the supercooling was 0-71" the time required for the mercury column to rise until, on observation through the telescope with the aid of the horizontal cross-wire, the ascent became imperceptible, was 92 minutes, as compared with about 3& minutes when the same milk was super- cooled 1-49'.It will be seen later that, in the absence of alcohol in the space surrounding the freezing-tube, the heat insulation of the milk is not perfect; a nett loss of heat occurs, for it is possible t o carry through a freezing-point determination under such conditions. The difference between the two methods of working- with and without alcohol-results in a longer time being required for the cooling of the milk when the space around the freezing-tube is occupied by air. There were also the difficulties of judging when the rising column of mercury had reached the highest point, due to the very slow movement which occurred in that region, and of getting satisfactory readings, owing to the short time that elapsed before a fall took place. The idea of following strictly the Hortvet technique, as regards stirring, for these particular experiments was therefore abandoned. In the first series of experiments, the results of which are recorded in Table 111, four or five stirrings of three strokes each were employed, and in the second series the mechanical stirrer, working at the rate of 40 strokes per minute, was in operation all the time, the thermometer rising until tapping became necessary. It does not appear that these variations in stirring caused any significant differences in the results obtained, but the times of rising of the mercury, after two different extents, large and small,

ISSN:0003-2654    

DOI:10.1039/AN9366100482

出版商:RSC    

年代:1936

数据来源: RSC

摘要:

OF MILK: CORRECTION FACTORS AND THE INFLUENCE OF STIRRING: I1 h I11 225 It was originally intended to employ four different amounts of supercooling for each sample of milk, vix. about 1.5, 1.0,0.8, and 0.5" C. It was found, however, that the differences in the readings of the thermometer corresponding to these different amounts of supercooling were in the neighbourhood of 0.002"-an amount so small that the unavoidable errors of observation might possibly approach the same order. It was, therefore, decided to employ only two different amounts of supercooling, as widely apart as practicable, say about 1.5" and 04", and to increase the number of samples examined. It was stated by Hortvet that, unless a much greater amount of supercooling than 0.5" is employed in the use of his cryoscope and technique, the rise of the mercury column is not sufficiently pronounced, and that there is more or less wavering, so that difficulty arises in deciding on the exact point at which the top of the column becomes stationary. Elsdon and Stubbs (Eoc.it.)^ found the same result when using a supercooling of less than about 0.8"; the mercury rose very slowly, and did not maintain a steady position for any appreciable time, and the proper freezing-point might not, under these circumstances, be attained. In the first experiments, made with the object of ascertaining the super- cooling correction, it was observed that where the amount of supercooling was small, that is, less than say 0-75", even in the absence of alcohol in the jacket surrounding the freezing-tube, the rise of temperature, when freezing occurred, was very slow-so slow, indeed, as to suggest doubts whether the thermometer would indicate the freezing-point of the milk, influenced only by supercooling, owing to the reading being affected by the length of time which elapses and the possibility of imperfect thermal insulation, causing a nett loss of heat from the freezing tube and contents.To give an instance; in an experiment when the supercooling was 0-71" the time required for the mercury column to rise until, on observation through the telescope with the aid of the horizontal cross-wire, the ascent became imperceptible, was 92 minutes, as compared with about 3& minutes when the same milk was super- cooled 1-49'. It will be seen later that, in the absence of alcohol in the space surrounding the freezing-tube, the heat insulation of the milk is not perfect; a nett loss of heat occurs, for it is possible t o carry through a freezing-point determination under such conditions.The difference between the two methods of working- with and without alcohol-results in a longer time being required for the cooling of the milk when the space around the freezing-tube is occupied by air. There were also the difficulties of judging when the rising column of mercury had reached the highest point, due to the very slow movement which occurred in that region, and of getting satisfactory readings, owing to the short time that elapsed before a fall took place. The idea of following strictly the Hortvet technique, as regards stirring, for these particular experiments was therefore abandoned.In the first series of experiments, the results of which are recorded in Table 111, four or five stirrings of three strokes each were employed, and in the second series the mechanical stirrer, working at the rate of 40 strokes per minute, was in operation all the time, the thermometer rising until tapping became necessary. It does not appear that these variations in stirring caused any significant differences in the results obtained, but the times of rising of the mercury, after two different extents, large and small,OF MILK: CORRECTION FACTORS AND THE INFLUENCE OF STIRRING: I1 h I11 225 It was originally intended to employ four different amounts of supercooling for each sample of milk, vix.about 1.5, 1.0,0.8, and 0.5" C. It was found, however, that the differences in the readings of the thermometer corresponding to these different amounts of supercooling were in the neighbourhood of 0.002"-an amount so small that the unavoidable errors of observation might possibly approach the same order. It was, therefore, decided to employ only two different amounts of supercooling, as widely apart as practicable, say about 1.5" and 04", and to increase the number of samples examined. It was stated by Hortvet that, unless a much greater amount of supercooling than 0.5" is employed in the use of his cryoscope and technique, the rise of the mercury column is not sufficiently pronounced, and that there is more or less wavering, so that difficulty arises in deciding on the exact point at which the top of the column becomes stationary.Elsdon and Stubbs (Eoc. it.)^ found the same result when using a supercooling of less than about 0.8"; the mercury rose very slowly, and did not maintain a steady position for any appreciable time, and the proper freezing-point might not, under these circumstances, be attained. In the first experiments, made with the object of ascertaining the super- cooling correction, it was observed that where the amount of supercooling was small, that is, less than say 0-75", even in the absence of alcohol in the jacket surrounding the freezing-tube, the rise of temperature, when freezing occurred, was very slow-so slow, indeed, as to suggest doubts whether the thermometer would indicate the freezing-point of the milk, influenced only by supercooling, owing to the reading being affected by the length of time which elapses and the possibility of imperfect thermal insulation, causing a nett loss of heat from the freezing tube and contents.To give an instance; in an experiment when the supercooling was 0-71" the time required for the mercury column to rise until, on observation through the telescope with the aid of the horizontal cross-wire, the ascent became imperceptible, was 92 minutes, as compared with about 3& minutes when the same milk was super- cooled 1-49'. It will be seen later that, in the absence of alcohol in the space surrounding the freezing-tube, the heat insulation of the milk is not perfect; a nett loss of heat occurs, for it is possible t o carry through a freezing-point determination under such conditions.The difference between the two methods of working- with and without alcohol-results in a longer time being required for the cooling of the milk when the space around the freezing-tube is occupied by air. There were also the difficulties of judging when the rising column of mercury had reached the highest point, due to the very slow movement which occurred in that region, and of getting satisfactory readings, owing to the short time that elapsed before a fall took place. The idea of following strictly the Hortvet technique, as regards stirring, for these particular experiments was therefore abandoned. In the first series of experiments, the results of which are recorded in Table 111, four or five stirrings of three strokes each were employed, and in the second series the mechanical stirrer, working at the rate of 40 strokes per minute, was in operation all the time, the thermometer rising until tapping became necessary. It does not appear that these variations in stirring caused any significant differences in the results obtained, but the times of rising of the mercury, after two different extents, large and small,

ISSN:0003-2654    

DOI:10.1039/AN9366100484

出版商:RSC    

年代:1936

数据来源: RSC