摘要:

THE ANALYST. MAY, 1S91. ~ - _ _ _ NOTE ON MALT VINEGAR. BY OTTO HEHNER. (Read at the Meeting, March, 1891.) ON several occasions samples of vinegar have been submitted to me with a view to ascertain whether they could be correctly described as malt vinegar. It is well known that much of the vinegar sold is either made from sugar or from specially prepared pyroligneous acid, such products being coloured with caramel, and possessing, when admixed with some real malt vinegar, to all appearance the properties of genuine malt vinegar. I am not acquainted with any directions to enable the analyst to distinguish these mixtures from the genuine article, and although I cannot pretend to have gone very exhaustively into the matter, the following analyses may yet supply E I Q ~ ~ slight help to other workerg in this field.82 THE ANALYST.Vinegar when prepared from malt must contain all soluble mineral constituents of the grain, whilst artificial vinegars are more or less devoid of ash, and almost wholly so of phosphoric acid. The solid matters of dry malt extract contain about from 07 to a 8 per cent. of phosphoric acid (P,O,), and a similar ratio is found in beers made from grain only, calculating in the usual manner the original gravity and the percentage of P,O, upon the original solids. I n the case of vinegar the original gravity cannot, as far as I am aware, be calculated with any degree of accuracy on acoount of the varying loss of alcohol and acetic acid which is almost unavoidable during the process of manufacture. If we add to the total solid matter found in a sample of vinegar the amount of sugar corresponding to the acidity, 120 parts of acetic acid corresponding in theory to 180 parts of glucose, the wiginal solids are certainly underestimated, and the percentage of phosphoric acid calculated upon these, therefore, correspondingly too high.But for the purpose of comparison, such a rough calculation will give sufficiently approximate wsults, as will be men from the following figures. Table No. I includes vinegars partly to my knowledge undoubtedly made from malt only, partly made by the best London manufacturers. TABLE I. Acidity . . .. I . . . 3.07 2.88 3.70 6.48 5.73 4-16 3.79 Total solids . . .. , , 3.26 2.72 4.01 2-44 2.46 1.68 4.23 Ash .. .. .. . . -39 *41 *31 -31 *47 *22 032 PBOS .. .. .. . . *13 -12 *13 -088 -092 so96 -067 Alkalinity (Na,CO,) , . ,. -072 -084 -037 *076 -089 ,017 *076 Calculated original solids . , 7.86 7-04 9.56 12118 l l * O E i 7 92 9-92 PzOK in original solids . * . . 1.65 1.70 1-36 -73 *83 1.21 -68 Samples 1, 2, and 3 are evidently made at so high a temperature that much loss of alcohol or acid took place, the proportion of phosphoric acid being extraordinarily high. Table 11. contains analyses of samples, some of which were acknowledged to be mixtures, but most having been bought as malt vinegar ; obviously none, except samples 8 and 9, were pure malt vinegars :- 8. 9. 10. 11. 12. 13. 14. 15. 16. Acidity . . . . 4.44 5.16 7.52 4.56 4.70 6.00 4.44 5.20 4.79 Total solids . . 1.23 2-30 -27 -6a 1.54 2.06 2.46 3.40 1.00 - -029 - -34 - - ~ 1 6 Ash .... Alkalinity .. - - none - *04S - 1. 2. 3. 4. 6. 6. 7. - - .. .. 0074 *098 trace -013 a018 *026 0026 -035 0026 -03 7 - - P A Original solids . . 7-89 10.04 11+5 7-48 8 52 11.06 9.12 11.20 8-18 P20K in original solids *94 -97 0 -18 -21 *23 028 -31 -32 by me in ANALYST, Vol. IV., p. 23. The phosphoric acid in all cases was estimated by the Molybdic method, as described DISCUSSION. Mr. CASSAL said that a limit of 3 per cent. of acetic acid had been fixed for vinegar, and if anything below that amount were found in a sample, a public analyst was justi- fied in certifying to adulteration. He understood that Mr. Hehner did not intend to convey that a watery solution of acetic acid of any strength was vinegar, and that he adhered to the 3 per cent.limit, He desired to ask whether the figures given repre- nented total acidity or acetic acid, and whether Mr. Hehner regarded the sample giving the figure 2.88 as a genuine malt vinegar j also whether the other samples could beTHE ANALYST. 83 guaranteed as being genuine malt vinegara. H e might mention that he had had some official cases of vinegar adulteration. H e had taken 3 per cent. of acetic acid as the basis for calculation, which was certainly low enough, and had certihd to minimum percentages of extraneous water. I n two cases, in each of which he had certified the presence of at least 30 per cent. of water, the reserve samples were sent to the Somerset House chemists, who had confirmed his certificates and had stated the same percentages.Mr. Cassal also wished to ask Mr. Hehner his reasons for calculating the original solids and referring the phosphoric acid to those solids. Dr. SYKES said that from the manner in which vinegar was manufactured nowadays, i.e., allowing a fermented malt wort to slowly trickle over twigs or shavings impreg- nated with the acetic ferment, contained in a vessel to which air had very free access, the whole process being conducted at a temperature of SOo to 90” Farht., naturally an enormOus loss of alcohol and acetic took place by evaporation; and he thought that this loss would quite account for the large amount of phosphoric acid the President had obtained, very much more malt extract being used up than the acetic acid in the sample mould represent, He did not think that sour beer could be used to any extent in vinegar making, since in sour ales there was usually besides the product of the acetic ferment, also the products of a number of unknown ferments, some of which were of an exceedingly nauseous character. H e thought the paper a most useful and suggestive one.

ISSN:0003-2654    

DOI:10.1039/AN891160081c

出版商:RSC    

年代:1891

数据来源: RSC

摘要:

THE ANALYST. 83 SOME FURTHER POINTS IN THE DETECTION OF ADULTERATION IN VINEGAR. BY Da. w. J. SYKES, D.P.H., F.Q;(.S, (Read at Meeting, A p i l , 1891.) IN thinking over our President’s paper, read before you last meeting, it occurred t o me that the nitrogenous constituents of a vinegar might afford some additional clue as t o its genuineness or otherwise. Malt, as you all know, contains a fairly large amount of nitrogenous matter varying under normal conditions from .some 8 to 13 per cent. About 45 per cent. of this is sohble ic water, and some portion of this ought to be found in the finished vinegar. Since all calculations made upon the constituents of malt; fomd in a vinegar must necessarily be based on the quantity of malt originally used in the preparation of that vinegar, it becomes neceesary-to ascertain first of all how close an approximation to this quantity can be found from an examination of the products formed by fermentation.In order to do this I shall have to touch briofly on the subject of vinegar manufacture. The first step in this process is tho preparation of the mash, which is effected by mixing intimately crushed malt and water heated to such a, temperature that the resultant mixture has a temperature of 140-145* Farht. The mash is allowed to stand until diastatic action is complete, the whole of the starch oE the malt being converted into soluble hydrolysation products, then the liquid portion, i.e., the wort is drained off. The wort, after being sufficiently cooled, is made to undergo the alcoholic fermen- tation by the addition of beor yeast.Homo makers, however, boil their wort first, by this means precipitating the dissolved albumen, and obtaining in this manner a brighter solution, On the other hand those makers who ferment the wort unboiled S ~ V Q the expense of firing, and no doubt secure tt better yield of alcohol. It has been shown by84 THE ANALYST. ~ Mr. H. Brown and Dr. H. Morris that in the process of mashing there are formed besides dextrin and maltose, a number of intermediary compounds of these two bodies, which have been named amyloi'ns. It is supposed there are some eighteen of tbese bodies, beginning with om moleculs maltose nineteen dextrin, two molecules maltose eighteen dextrin, and so on until nineteen maltose and one dextrin is arrived at.The members of this group which contain most dextrin are said to be unfermen- table by the Saccharomyces Cerovisiae, but can be completely broken down by diastase to fermentable maltose ; consequently the manufacturer who ferments his wort unboiled leaves his diastase intact, and this gradually converts the amyloi'ns ioto a sugar capable of being fermented completely away. The alcoholic wort, freed as much as possible from yeast, is now subjected to the action of the acetifier. This is a vessel with a false bottom perforated with numerous fine holes situated some inches above the r e d bottom. A few inches from the top of the vessel, what may be called a '' head," perforated with very fine holes, is fixed. The intervening space between the head and the false bottom is filled with twigs or wood shavings impregnated with the acetic ferment.The alcoholic wort is placed in the space above the head, and passing through the fine holes in it, slowly trickles over the acetifying material. Free aeration is obtained by a number of holes bored all round the vessel immediately below the head, and also immediately above the fahe bottom. The partly acetified wort collects in the lower part of the vessel below the false bottom, from which it is returned to the upper portion of the vessel, and thus made to traverse the acetifying material again and again, until acetification is complete. The process is carried on at a temperature of SOo Farht. This free aeration and high temperature naturzlly leads to much loss of alcohol and acetic acid, and ail sorts of schemes have been and are being tried to reduce this loss.It is found in practice that a wort of 1055 specific gravity .yields upon fermentat- tion about 7 per cent. of alcohol ; this upon acetification should yield theoretically 9.1 per cent, of acetic acid. But, working under the most favourable circumstances, it is never found to yield more than 6 per cent., consequently a loss of over 34 per cent. takes place, If the process is carried on in a less efficient manner, the loss is considerably higher, the yield not unfrequently amounting to but 50 per cent. of the theoretical one. Since ten parts of malt mashed in one hundred parts of water give a wort of a gravity of 1025-27 ; taking the lowest of these figures, 22 per cent. of malt would give B wort of 1055 specific gravity; and as this, if worked under the best conditions, pro- duces a vinegar containing 6 per cent.acetic acid, in this case one part of acid would correspond t o 3.7 parts malt. Under less favourable conditions of working it might represent 4.9 parts malt. Therefore we cannot go far wrong in assuming that a t least 3-7 per cent. of malt has been used for every per cent. of acetic acid found in a vinegar. The nature of the nitrogenous contitituents of malt now claim a brief notice. The grain of barley consists of two portions, the ondosperm or reservoir of reserve materials from which the young plant contained in the exosporm is to derive its supply of nutri- ment, until able to derive its nourishment fIom the inorganic constituents of the air and soil.The starchy and albuminous matters are present in the endosperm for the most part in an insoluble condition, and before they can be of us8 for the nourishment of theTHE ANALYST. 85 young plant, must not only be dissolved but converted into a form capable of passing by diffusion through the walls of its cells. For this purpose certain enzymes or fer- ments are present, which apparently act in a manner extremely analogous to that in which the animal digestive ferments act. Thus diastase acts upon the starchy portion in the -me manner as the ptyalin of the saliva, converting it into maltose and dextrin. A similar digestive process apparently takes place with the nitrogenous bodies, bui so far the ferments causing these changes have not yet been isolated.Much work has lately been done in the examination of theaction of the digestive ferments upon animal albuminous matter, and this points very strongly to the fact that the digestion of albu- minous matter is a process of hydrolysation, treatment with the mineral acids, caustic alkalies and steam under pressure yielding the same products as digestion by ferments. If a mass of coagulated egg albumen be placed in a large quantity of a solution of pepsin acidulated with hydrochloric acid to the extent of 0.2 per cent., and the whole kept a t 100 per cent. Farht., in a very short time the whole will be dissolved. If at this point a portion of the solution be neutralised nearly the whole bulk of the albumen will come down, and on furthur addition of alkali it will dissolve ; the albumen has been changed into acid-albumen or syntonin, and is now insoluble in a neutral solution as the original albumen was.If in the original solution digestion be carried on for a period of twenty-four to forty-eight hours and a portion be neutralised as before, only a small precipitate will appear, and on boiling no further precipitation occurs. If, however, the solution be saturated with ammonium sulphate nearly the whole of the albuminous matter will come down; it has undergune a further change, and is now in the condition of albumose. On carrying on digestion for a considerable longer time-several days-a a stage is reached when the saturation of the solution with (NH), SO, no longer causes precipitation, The albuminous matter is now capable of diffusing (though slowly) through a cell wall; it is in the form of real peptone.This seems as far as the ferment pepsin will take a solution of albumen, more powerful hydrolysts, such as caustic alkalies and mineral acids, carry on the process still further, a number of amide bodies being first produced, and further on the whole albuminous matter being broken up into far simpler forms, such as ammonia, carbonic anhydride, urea, etc. If a solu- tion of peptone be made strongly alkaline by caustic soda or potash, and a few drops of an exceedingly dilute solution of copper sulphate be added, a beautiful rose-red colour is produced ; this is the well-known biuret reaction which has been considered until lately as characteristic of peptone.It is found, however, to be given by both albumen and albumose, in a somewhat modified form, the calour inclining to violet. Several inorganic compounds also form excellent tests for the various digestion products of albumen, thus potassium ferrocyanide and acetic acid, potassio-mercuric iodide in slightly acetic acid solution precipitate albumen and albumoses but not peptone. Phospho-tungstic acid in strongly hydrochloric acid solution, potassio-bismuthic iodide in slightly HC1 solution, and tannin precipitate the whole of the three groups; an excess of tannin, however, redissolves the tanno-peptone precipitate. The process of malting consists essentially in arousing the dormant vital povers of the barley corn into activity and then again arresting them. One of the first forms of activity displays itself in the secretion of various enzymes or ferments ; the first action86 THE ANALYST.being todissolve the cellulose of the cells containing the stuch, the starch itself is ah0 altered to some extent in the direction of soluble starch. Considerable action takes place with regard to the nitrogenous constituents, about twice as much of these are soluble in malt as were soluble in the original barley. The grouping is also different, of one hundred parts of nitrogenous matter in barley sixty-three parts belong to the albumen group, and thirty-seven parts to the amide; in one hundred parts malt forty- six parts belong to the albuminous group, fifty-four parts to the amide. It must be noted that hydrolytic action goes further here than in animal digestion, albuminous matter being evidently converted into the amide form with great ease.The amides being crystalline bodies naturally possess a much higher rate of diffusion than peptones, and are thus able to move about the grain more freelv. If a quantity of malt be mashed in the ordinary manner, the wort filtered off and then boiled, the bulk of the albumen precipitates by coagulation; if the clear filtrate be saturated after cooling with ammonium sulphate, an abundant precipitate forms. This precipitate, which, so far as I know, has never been described before, coming down as it does under the same conditions that the albumoses do in the animal diges- tion, I propose to call by the same name. If the filtrate from these be diluted with an equal bulk of water, and a small quantity of Alumh's tannin solution" added, after standing twenty-four hours a very small precipitate of peptone will be observed. Real peptone occurs in malt only in very small traces.The albumoses can be easily esti- mated by washing with saturated ammonium sulphate solution, the precipitate obtained by saturating a solution with the same aalt, drying on a tared filter, and afterwards estimating the ammonium sulphate clinging to the precipitate and filter. The albumoses are not diffusible, and are incapable of nourishing the yeast cell j this I have ascertained experimentally ; yeast will not increase in a solution of dextrose with the proper mineral constituents if albumose be the only nitrogenous compound present. They therefore appear in the wort after it has undergone the alcoholic fermentation, and also in the finished vinegar, the bacteria of acetification not completely removing them. Conse- quently a vinegar prepared from malt always gives a precipicate on saturation with ammonium sulphate j also on the addition of phospho-tungstic acid, or of bismutho- potassic iodide, or mercuro-potassic iodide, and with tannin. The amide constituents are undoubtedly the ones which supply the yeast and bacteria with nitrogenous food, and are consequently seriously diminished in quantity.Besides the nitrogenous groups abeady mentioned, there k st21 another oiie present in malt-the gluten group consisting of throe members, gluten-casein, gluten- fibrin, and mucedin. All these are more or less soluble in dilute alcahoi, and in slightly alkaline or acid solutions.Since all malt worts contain more or less lactic acid, a certain portion of these bodies must go into solution. By long continued boiling they are converted into a coagulated insoluble form. In their chemical reactions they closely resemble the albumoses. Vinegar, after complete acetification, is heated in order to sterilise ; at the same ~~ ~ ~~ ~ ~~ ~ ~~ * This exceedingly delicate test for peptoneis prepared by dissolving 4 grams. of tannin in 190 C.C. of 60 per cent. alcohol with the addition of 8 C.C. of 26 per cent, acetic acid. One part of peptone in 100,000 pts. of solution gives a perceptible turbidity, and 8 precipitate after standing twenty-four hours. Excess of precipitant must be avoided.TEE ANALYST. 87 time certain salts more soluble in hot solution than cold are added.These re-precipitate in the course of twelve or fourteen days, carrying down with them the suspended impurities and a portion of nitrogenous matter; in fact these salts act as a sort of mineral finings. In estimating the mineral constituents of a vinegar it must be borne in mind that lime mlb are often added to the water employed in mashing to secure a more brilliant wort. Also that various kinds of yeast foods containing large amounts of phosphates are often added to the wort with a view to stimulate yeast production and secure B higher production of alcohol. Various malt substitutes are also frequently employed in vinegar manufacture, such as unmalted barley; a number of gelatinised preparations are also in the market made from rice and maize; the use of all these would slightly lower the percentage of soluble nitrogenous matter in the wort and finished vinegar.Sugar is also employed, and if used in any quantity would seriously lessen the quality of nitrogen found in the vinegar. I found in a vinegar which I had every reason to suppose genuine 6.5 per cent, of acetic acid; this figure multiplied by 3.7 would give 24-05 per cent. malt originally used. Assuming the malt contained 10 per cent. (the average amount) of soluble nitrogenous matter, of which on an average 45 per cent. is soluble, the wort would have contained 1.08 per cent. soluble nitrogenous matter. The vinegar contained 0.49 per cent. nitrogenous matter, consequently the wort had lost rather less than one half during the processes of conversion into vinegar.The albumoses amounted to 0.213 per cent. It gave an abundant precepitate with all the before mentioned reagents. From this it follows, I think, that considerable information may be gathered from an examination of the nitrogenous constituents of a vinegar as to whether it is genuine or not; but the fixing of limits must naturally be reserved until B long series of experi- ments have been performed in this particular direction. In conclusion, I beg to acknowledge my indebtedness t o a series of papers by Mr. J. A. Nettleton, F.C.S., now appearing in the Brewers’ Journal on the manufacture of vinegar. DISCUSSION. The PRESIDENT said that, in his opinion, the custom to lump certain constituents of’ allied composition together had had a retarding influence upon the progress of our’ knowledge of food.It was convenient, but unscientific, to calculate, for instance, from the nitrogen the amount of nitrogenous matter, without stating what nitrogenous mattem were present, and in what proportions. Such calculation was even frequently very inaccurate, as had been shown, among others, by the late Nr. Wigner in his researches on the nitrogenous constituents of wheat and cocoa. He (Mr. Hehner) was therefore grateful to Dr. Sykes for attempting B discrimination of the albuminoids in the present instance, and for the summary of methods applicable to this object. He hoped that ultimately we would obtain a thorough differentiation of these substances in all article8 of food.Professor WYNTER BLYTH said that 75 per cent. of Dr. Sykes’s paper could be found in any chemical primer, but the remaining portion was interesting and im- portant, for there Dr. Sykm showed that the nitrogenous constituents of vinegar could be divided into groups. It was, however, to be regretted a more extensive Series of88 THE ANALYST. experiments had not been made, so as to determine the quantity of each nitrogenous group in genuine and spurious vinegars. It would seem that in only one case had this been done. In making a similar investigation on organic fluids, he had found Kjeldahl’s process peculiarly applicable, for total nitrogen in the whole could be deter-. mined, and then precipitants, like phospho-tungstic acid, could be applied, and the nitrogen in the filtrate determined by Kjeldahl and subtracted from the total nitrogen, thus giving the nitrogen in the precipitate. He had long held the opinion that the only possible way to accurately determine food values was to pass that food through the human intestine in the simplest form, and first to analyse that which goes in (income) and then that which goes out (output). That had been done in a few instances only, but it was the only scientific method of arriving at the value of a food. Dr. SYEEB, in reply, said that the reason he had introduced the subject of animal digestion into the paper was to illustrate the similarity between it and the action o€ the enzymes upon the proteid matters in germinating barley; With reference to tho various reagents he had mentioned, he did not think they were so universally known as Mr. Blyth had suggested. As to the method of estimating the various proteid pre- cipitates by the Kjeldahl process, he had employed this method for some time past. I n order to obviate the frequent breakages which occurred in distilling off the ammonia in Kjeldahl’s process, where the liquid contained tungstic acid in suspension, he made use of a tin flask, which answered the purpose perfectly.

ISSN:0003-2654    

DOI:10.1039/AN8911600083

出版商:RSC    

年代:1891

数据来源: RSC

摘要:

88 THE ANALYST. THE DETECTION OF BUTTER ADULTERATED WITH COCO-NUT FAT. BY DR. JOHN MUTER, F.R.S.E., F.I.C. (Read at Meeting, April, 1891.) THE ever increasing tendency to scientific adulteration teaches us the necessity of not judging the purity of butter by any single one of the accepted tests. Until some time ago the Reichert process, or one of its modifications, was considered sufficient for all ordinary purposes ; and still more recently the use of the oleorefracto- meter has been declared to be all that is necessary. Now, however, we have the advent of an inventor who is able to take away all taste and odour from coco-nut fat, and thus to render it available as an adulterant where there is a quick sale. To a certain extent it may be used to defeat the ‘( Reichert,” because, taking an average good butter, the distillate from which will absorb 14.0 C.C.of decinormal soda, and an average sample of coco-nut fat which will yield a distillate consuming 3.5 c.c., we notice that each 5 per cent. of the latter fat added to butter wiii oniy reduce the soda useci by about *GO c.c., and i t is thus possible to adulterate to the extent of SO per cent., and yet the butter will pass the 12 C.C. limit ; while, if we are to take account of the famous Danish butter and those exceptional samples brought to our notice by Dr. Vieth, we could have a 40 per cent. adulteration passing with impunity by the Reichert process. This is bad, but the refractometer is in a similar position, because if we take one-half COCO fat and one-half margarine, we can make an article that shows a refraction of -33, and thus comes out pure butter. I had, in common with our President, been struck with the fact that there was so much cheap butter about that just showed exactly 12 C.C.with Reichert, and I set myself to solve the mystery, because the use of the small quantity of ordinary margarine necessary to make this reduction would scarcely repay the labour of the manufacture. After someTHE ANALYST. 89 research I came across several samples absorbing 12 C.C. of soda, and which when examined in the refractometer came out far too good, and I then saw that the key to the whole affair was that the use of coco-fat by the adulterator must be met by the joint employment of both the refractometer and the Reichert on every sample.Given the use by the analyst of both these tests, then the mixing of butter with 25 per cent. of coco- fat, and its passing us as standard butter, will be a thing of the past. In illustration of this I give a few figures of some mixtures that were made with care, and the analysis divided between two persons who did not know what the samples were. The u Reichert ” process was done by Mr. Burford, of Leicester, one of my pupils, who is now working on to get his Institute diploma, while the refractions were done by myself. Nature.of Sample, Reichert. Refraction. Experiment 1. All coco-nut fat .. .. 3.5 C.C. -54 ,, 2. Pure butter of good quality . . 14.5 C.C. -34 ,, 3. Butter with 75 per cent. ccco 6.0 -49 Y, 4. 9 , 50 ?J 9 , 9 0 -44 93 5. 9 , 25 9 9 27 12.0 -39 The refraction of the coco-nut fat is so great; as to be beyond the scale of the ordinary instrument, and has therefore to be got by using a half-and-half mixture with (( typical oil,” which shows - 27.Nature of Sample. 7. Butter with 75 per cent, margarine Experiment 6. Margarine . .. .. .. 9 , 8. 7 9 50 7 9 Y, 2, 9. 9 , 25 Y, 9 9 ,, ,, ,, ,, 10. Margarine with 50 per cent. coco. . 11. Butter with 25 per cent. margarine ), j 12. Butter with 50 per cent. margarine and 25 per cent. coco-nut fat and 25 per cent. coco-nut fat Reichert. 1-3 C.C. 4.5 C.C. 7.8 C.C. 10.9 C.C. 2.8 C.U. 8.8 C.C. 5.6‘c.c. Refraction. -8.5 -15 0 -22.0 -27.0 -3 2.0 -33 -27 The margarine used was that now commonly sold in London, and contained some vegetable oil, probably cotton, thus lessening its refraction, that of pure beef oleo- margarine being generally - 1 3 O .It is thus evident that while each 5 per cent. of coco-nut fat added to butter increases its left-handed refraction by one degree, while it reduces the soda consumed in the Reichert process by *50 per cent. If, therefore, I had a butter showing a refraction of 37 and a Reichert of 12, I should have no hesitation in charging it with 20 per cent. of coco-fat. Mixtures Nos. 5 and 9 would pass by a Reichert limit taken on the lowest recorded natural butter, but they are caught by the refraction; while Nos. 10 and 11, which would defeat the refractometer, are at once detected by Reichert. There is a decided relation between the refraction and the Reichert indication of all pure butters. The highest refraction I ever met with was in a butter showing -36. I naturally suspected coco-€at, but on applying Reichert I got the large result of 16 C.C. I am now engaged in verifying this relationship, and I put forward the following figures tentatively as a basis for others to take up the matter.90 THE ANALYST. Refraction. -36 -35 -34 -33 -3 2 -31 -30 -2 9 Reichert. 16 15.25 14.50 13.75 13.00 12.25 11.50 10.75 When we have to deal with butter reduced by margarine this steady relation fails, and we have (as in experiment 9) a drop in the refraction. This matter I put forward tentatively only at the moment, in the hope that it will work out to a useful indication.

ISSN:0003-2654    

DOI:10.1039/AN8911600088

出版商:RSC    

年代:1891

数据来源: RSC

摘要:

90 THE ANALYST. MEASURING MILK FOR QUANTITATIVE DETERMINATIONS, BY DR. I?. T~IETH. (Read at Meeting, April, 1891.) IF the first consideration of the analytical chemist in executing his practical work always must be to arrive at reliable and correct results, there is no reason why the second consideration should not be to obtain these results in the most convenient manner. I have, for years, been in the habit of measuring by meansof specially gauged pipettes the quantities of milk required for the determination of total solids, ash, and fat. That it requires less time and is less troublesome to pipette 5 grams. of milk, than to weigh a corresponding quantity, nobody will deny, and I have adopted and adhered to the more convenient way of measuring a f e r having satisfied myself that with ordinary care no inaccumcies occur which could not be safely neglected.When a short time ago, on my mentioning the subject in this room, doubts were expressed whether measuring milk for quantitative determinations was admissible, I resolved to make a systematic series of experiments. The figures, which, with your permission, I am going to submit to you are the results of the investigation. On the day on which the experiments were carried out the lowest specific gravity observed in any of the milk samples at hand was 1.0315, and the highest 1.0330. These two samples were used, as was also a third sample, reprosenting the mixed yield of a number of dairies, and exhibiting a specific gravity of 1.0325. The temperature of the three samples was brought successively to 48, 60, and 75*F., and quantities were pipetted off and weighed, a pipette being used which was supposed to deliver 5 grams.of milk of the average specific gravity of 1.032 at a medium temperature of 60QF. The weights of the measured quantities were follows :- Sample. I. 11. III. Specific gravity . . .. .. . . 1.0315 1,0325 1*0330 Temp. 48OF. , . .. .. .. 4.987% 5.003 5.002 4.998 5.001 5.003 4.997 5.001 5.002 Temp. 60QF. . . .. .. .. 4.993 5.001 5-001 4.993 5.001 5.002 4,994 5.002 5-001 Temp. 75OF. .. .. .. .. 4.990 4.991 5-001 4.993 4.985* 4.997 4.990 4.990 4.998TI3CE ANALYST. 91 That specific gravity and temperature are not without some influence is clearly proved by these figures, which show that influence in the direction in which one would expect to find it, the smallest weight of milk being obtained when the specific gravity was lowest and the temperature highest, and the largest weight when the specific gravity was highest and the temperature lowest.As a rule the three quantities measured under equal conditions agree very well ; there are, however, two exceptions-they are marked with asterisks-representing the inaccuracies which, perhaps, cannot be entirely avoided when working with pipettes. Of the twenty-seven quantities measured the smallest weighed 4.985, and the largest 5.003. If we take these two extremes and suppose that we were dealing with a milk containing 11.50 per cent. total solids and 3.00 per cent. fat, instead of these per- centages we would find in the one case 11.47 and 2.99, and in the other 11.51 and 3.00.Working upon a milk with 14.00 per cent, total solids and 5@00 per cent. fat, the results would be 13.96 and 4.99 in one instance, and 14.01 and 5100 in the other. The conditions under which the above samples were taken are about as different as one would ever expect them to be, and the influence of the inaccuracies introduced by meamring the quantities required for the determinations is so small that, I think you will agree with me, it may be disregarded. I f that is so in the case of normal milk samples, the question still remains open what the results would be when one has to deal with abnormal samples. The further experiments were made with a view to answer this question ; the various samples were kept at the temperature of 60°F.Three quantities measured off weighed 5.038, 5.043, and 5.040. Taking the highest weight, viz., 5.043, and supposing the ample to contain 9.60 per cent, total solids and *40 per cent. fat, the results found mould be 9.68 and *40. I next mixed two parts of milk with one part of water ; three measured quantities weighed 4.955, 4.961, and 4.960. Supposing the mixture t o contain 8-60 per cent. total solids and 2.60 per cent. fat, the result by taking the smallest quantity of 4.955; would be 8.52 and 2-58. Of a mixture of two parts of milk and one part of a thin cream the pipetted quantities weighed 4.943, 4.946, and 4.945. I did not analyse the mixture, but it must have contained as near as possible 19.00 per cent, total solids and 10*50 per cent. fat. Using 4.943 grams.for the quantitative determinations, 18-78 and 10.38 per cent. respectively would be found. In this instance, then, we have a difference which cannot very well be neglected. Lastly, I took a square-shaped six-ounce medicine bottle, put five ounces of milk in, and shook it well each time immediately before drawing off the quantities t o be weighed. Pushing the pipette right down to the bottom I obtained 5.012 and 5*008. The stem of the pipette was, of course, wetted with milk outside to a length of about five inches. By repeating the experiment with the only alteration that I wiped the pipette after withdrawal from the bottle, the quantities were 4.990 and 4.981. Pushing the pipette half way down, the quantities weighed 4.980 and 4.979; and taking the samples from one-half inch below the surface 4.971 and 4.969 grams. were obfrtined. I took a skim milk of specific gravity 1.0360. I92 THE ANALYST. These latter quantities were increased by leaving the bottle undisturbed for one and a-half minute to 4.985, for three and a-half minutes to 4.991, and for five minutes to 4.999. Although there is nothing in these experiments which everyone of you could not try for himself any day he liked, I thought it not out of place to put the figures before you, well knowing from personal experience that one does not always find leisure for and pleasure in clearing up even very simple questions.

ISSN:0003-2654    

DOI:10.1039/AN8911600090

出版商:RSC    

年代:1891

数据来源: RSC

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92 THE ANALYST. FAT EXTRACTION FROM MILK-SOLIDS. BY ALFRED W. STOKES, F.I.C. Read at &feetifig, April, 1891. Though fat can be the most readily and accurately extracted from milk in its liquid form in the manner pointed aut by Dr. Hill in the last number of the ANALYST, yet occasionally it may be newssary to determine the fat on the dried milk residue. It may happen that after putting on a portion of the milk for total-solids the rest may be spilt, or the original quantity may be exceedingly small. I n such cases both the total-solids and the fat may be separately and accurately determined on only 5 grammes of the milk thus :- First, dry to constant weight 5 grammes of the milk in a platinum, porcelain, or glass dish, and weigh as usual for total-solids. Now moisten the milk-solids with from 5 to 8 C.C.of strong HCl, cover the dish with a cover-glass, and leave it on the water- bath for from three to five minutes. With a rubber-covered glass rod well break up the contents of the dish. Wash this with hot water into one of the tubes Messrs. Townson and Mercer make for me for the Schmid process (the shorter or old form.) Fill with water to the 20 C.C. mark. Cool. Wash the dish out with ether into the tube, and fill this up to the 50c.c. mark with ether, Shake vigorously three times at intervals of three to five minutes. Then let settle, pipette off 20 C.C. of the ethereal solution into a weighed dish. Evaporate off the ether from this, and weigh the residual fat. Lastly note the quantity of ethereal solution left in the tube, and calculate accordingly.Much more fluffy material marks the junction of the ethereal solution and the dark brown acid liquid than in the ordinary Schmid method. But this material is more apparent than real; it is usually correct to allow only 0.5 C.C. for this, however bulky it may be. There is not the least diffculty in pipetting off t.lm ethereal solution. Even in summer it is only necessary to hold the tube for half a minute under the tap to cool it, and then the ether can be dealt with as leisurely and accurately as so much water. Swinging the tube round at arm’s length wili more rapidly separate the ether from the mid liquid. The method otherwise is such as is detailed in Chemical News, of November lst, 1889. The results obtained are evidenced in the following list of the whole of the samples thus analysed during the last twenty-one days.In some cases the fats were also determined by the Schmid method on the liquid milk. For comparison I give the results calculated from total-solids and specific gravity using the admirable table of Messrs. Hehner and Richmond (ANALYST, Vol. xiii. p. 26.) The sp- grs. were taken by the Westphal balance, and the total-solids were dried to constant Cork the tube, The results agreed.THE ANALYST. 9s Total Solids. ~ ~~ ~ weight. were not specially prepared, but were received in the ordinary coume of work. works aa well with poor as with rich milks. I append the total-solids merely to show the sort of milks dealt with, they I have arranged them in the order of quantity of fat, showing that the method Fat Calculated.I Fat Found. I I 6128 10.91 10*12 11.06 9-90 10.78 11.90 10.95 11.63 11.97 12-89 12-56 1.46 2.56 2.79 2-80 2.84 2.84 2.97 3-03 3.28 3.57 3.84 3.87 1.47 2-60 2.80 2.74 2.85 2-89 2.98 2-97 3-23 3.51 3-87 3.89 Here, the differences between €at found and calculated range from + 005 to -*06, the average being 002. A sample of stale milk twenty-one days old gave by this method 3.09 fat, and by Sohmid method on the stale but liquid milk 3.01. Here the main difficulty is in taking a correct sample, hence the larger difference. Some of these results were obtained by my assistant, Mr. W. N. Yarrow, to whose careful work I am greatly indebted, and some by myself. Mr, A. H. Allen’s suggestion to pipette off as much ether as possible, then fo shake with some more ether, and add this to the former quantity would, I think, obviate thedffficulty found at times of reading off the quantity of ether left in the tube. But it would also about double the time taken by the whole operation. By an apparatus I am now constructing I think it will be possible to take the specific gravity on 5 C.C. of milk. So that accurate determinations of total solids, fat and specific gravity may all be made on the same 5 C.C. of milk, if necessary, (Conclusion of the Society’s Proceedings.)

ISSN:0003-2654    

DOI:10.1039/AN8911600092

出版商:RSC    

年代:1891

数据来源: RSC

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THE ANALYST. 9s TESTING OF COMMERCIAL TOLUIDINE." BY F. F. RAABE. EVEN in the aniline trade the necessity has been felt of late years to sell pure products with guaranteed analysis, particularly in the case of aniline and tolhdine. At one time most of the toluidine offered for sale was tested by the buyers a,s to its specific gravity and boiling point, but now they demand a specified percentage of p toluidine. The estimation of this body in presence of o toluidine and aniline often leads to disputes with the manufacturers, because the testing is not always done precisely in the =me manner. cliem. f i t . , Nos. 8 and 12, 1891. (Slightly abridged.)94 THE ANALYST. The aniline works which obtain their benzol, 50-90 per cent., from England, know that they must exactly stick to the specification or contract.This provides for the size of the retorts, length of the condenser, distance of thermometer from bottom of retort, etc., etc., in order to get concordant results. To prevent as much as possible analytical diflerences in the testing of toluidine, it is absolutely necessary for the buyers to agree with the manufacturers on a definite method of testing. As I have lately been often consulted as to a reliable process for the estimation of p toluidine, I will now communi- cate the various methods from time to time proposed. In testing toluidine, one must take particular notice of its appearance, which should be as clear as a brewer likes to see his ale. The colour may, however, be spoiled to some extent when the sample has been stored in iron barrels.To ascertain the boiling point, and consequently the pre- sence of higher homologues, 100 C.C. of the oil are fractioned in a retort holding about 180° C., the heat being so regulated that about two drops distil over every second. The specific gravity is taken with the bottle, or also very accurately with a large hydro- meter, by preference the one devised by Lunge. To get the temperature exactly at 15* C., the oil is put into a cylinder, which is then put into a second cylinder, filled either with warm or, if necessary, iced water. For the estimation of p toluidine many processes have been proposed, and the method to be chosen ought to be such a one as can be readily mastered by the most in- experienced who works on not too small quantities of the sample. Merz and Weith take advantage of the little solubility of p toluidine in water, which process was further worked out by Schoop.Rosenstiehl noticed the little solubility of p tdluidine oxalate in ether, which process was simplified by Nietzki, and particularly by Lorenz. Lunge recommends the taking of the specific gravity, and has published an excellent table; whilst Schiin treats the sample with potassium dichromate and hydrochloric acid, and then tests colorimetrically. I have tried a totally new idea, which consisted in dissolving p r e p toluidine in the sample and ascertaining the solidifying point of the mixture. I cannot recommend the colorimetric process, as this is too much influenced by the personal equation in working. The specific gravity process is very much influenced by slight alterations in tempera- ture, and also by the presence of small quantities of aniline.Schoop’s acetyl process may be used when the sample is of at least 30 per cent. strength, by operating as follows :-The toluidine must have been dried with calcium chloride or potassium carbonate. Ten grams. of the sample are boiled, under a reflux condenser, with 10 C.C. of acetic anhydride, After cooling, 30 C.C. of glacial acetic acid are added, and the mix- ture poured into 400 C.C. of hot water, the flask being rinsed with another 200 C.C. of water. The liquid is then kept for twenty-four hours at a temperature of O* C., which causes $he rreparafion of acettoluidine, which may be collected on a weighed filter, slightly washed with dilute acetic acid, dried first by pressure between blotting paper, and finally at a temperature of 98* C.149 parts of the precipitate correspond with 107 parts of p toluidine. The oxalate process is most conveniently performed according to Lorenz’s directions. If applied in an empirical sort of way, the results are very good. What is wanted is pure ether, free from alcohol and water ; a solution of 1.062 grams. of dry oxalic acid inTFKE ANALYST. 95 250 C.C. of ether; deci-normal solution of carbonate of soda ; pure o and p toluidine, and also very delicate litmus paper. First of all, 10 C.C. of the ethereal oxalic acid solution are put into a flask containing 25 C.C. of water, and, after removing the ether by distil- lation, the residue is titrated with the sodium carbonate, litmus paper serving as indicator.Two grams. of pure p toluidine are now dissolved in '70 C.C. of ether, with two drops of o toluidine and so much of the oxalic acid solution added until all the p toluidine is precipitated, which may be easily recognised by the turning red of litmus paper. After adding another 2 C.C. of the acid, the whole is allowed to stand for four hours at a temperature of 158 C., when the precipitated oxalate is filtered off and washed with about 30 C.C. of ether, both filtrate and washings being collected in a flask containing 25 C.C. of water. The ether is distilled off, and the residue again titrated with the soda, when the difference between the two titrations will give us the check on the oxalic acid, which may then be used to test the commercial sample. I have tried to use a watery solution instead of the ethereal one, and have obtained very satisfactory results when analysing samples containing from 25-40 per cent.of toluidine. The acid must, however, be added in large excess, and the precipitate weighed. After a few more experiments, 1 hope to say something more on the subject. The solidifying or crystallisation process is, however, a much quicker one. When the sample is fuaed with from 1-3 parts of pure toluidine, a mixture is obtained which may be tested by taking its solidifying point. With the same weight of pure p toluidine, the percentage of the mixture is got accurate within 05 per cent., with double the weight *33 per cent,, with treble the weight *25 per cent. For instance :- Difference. 10 Toluidine of 50 per cent. p + 10 purep = 20 Toluidino 75 50 ,, + 10 ,, = 20 ,, 75.5 ,, - 10 ?) 10 9 , 30 1 ) + 20 ,, = 30 ,, 76.66 ,, -33 10 9 , 31 ,, + 20 ,, = 30 ,, '77 10 Y, 30 ,, 3- 30 ,, = 40 ,, 82.6 :: 026 31 ,, + 30 ,, = 40 ,, 82.75 ,, - 10 $ 9 per cent, 95 - A 30 C.M. thermometer, running from 30-50° C. and graduated in ino, shows a difference of *2 per cent. of paratoluidine. The process 2, therefore, very suitable for being daily used by manufacturers. It is as well to have at hand a number of standard samples, containing, sag, 82.5, 83, 83.5, 84, 84.5, and 85 per cent. of p toluidine, to be compared with any given sample. I will Ia,ter on communicate in how far the crystallkation point is influenced ~ J V presence of any moisture.

ISSN:0003-2654    

DOI:10.1039/AN8911600093

出版商:RSC    

年代:1891

数据来源: RSC

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TFKE ANALYST. 95 THE ELECTROLYSIS OF METALLIC PHOSPHATES IN ACID SOLUTION. BY EDGAR F. SMITE.* IN a former article, bearing the above title, I showed that copper and cadmium could be precipitated electrolytically from solutions of their phosphates. Their separation from each other was also noted, as well as the separation of the individual metals from iron, aluminium, chromium, zinc, nickel, and cobalt. Further, the separation of copper from manganese was shown to answer all practical requirements. The free phosphoric acid, present in the solution, prevented the deposition of the manganese as dioxide. * dmericart chemica2 JownsZ,96 THE AJYALYST. Since reporting this last separation I have found that cadmium can be separated from manganese electrolytically without any particular difficulty.Cadmium from Manganese. When I electrolysed the acid phosphates of copper and manganese, 10 C.C. of phos- phoric acid (sp. gr., 1.347) were present in the solution. The current employed gave 0-10 C.C. OH gas per minute. In the presence of such a large exces of acid, cadmium was not precipitated by a, current yielding 10 C.C. OH gas per minute. It therefore became necessary to know just what quantity of free acid could be present in the solution and the cadmium be entirely deposited. The quantity of acid requisite for the retention of the manganese was of importance. Several trials led to the following con- ditions as being best suited for the complete weparation of the metald under discussion : 1. 10 C.C. cadmium sulphate solution (= 0.3399 gram. cadmium), 10 C.C.manganese sulphate solution (= 0*1000 gram. manganese), 20 C.C. disodium phosphate (sp. gr,, 1-OSSS), 3 C.C. phosphoric acid (sp. gr., 1*347), and 100 C.C. water were electrolysed with a current liberating 10 C.C. OH gas per minute. In twelve hours 0.2394 gram. cadmium was precipitated. Not the slightest deposition of manganese dioxide was observed upon the anode. 2. In this trial the conditions were precisely the same as those given in 1. The deposit of cadmium metal weighed 0*24@0 gram. It will be noticed that the error in the results is fully within the limit. Cadmium wm not detected in the filtrate. The deposits in both experiments were very crystalline. Hot water was employed in washing the metal. The current was invariably increased for about an hour beforeits final interruption.The acid liquid was syphoned off from the metallic deposit before the vessel in which the precipitation occurred was disconnected. Some OF the heavier metals were studied in the same manner as copper and cadmium. They are new and have value for the student of electrolysis. The drying was done upon a warm iron plate, The results of this study are given bslow. Platinum. 0.2590 gram. of ammonio-platinum chloride was dissolved in water. To this solution I added 30 C.C. disodium phosphate (sp. gr., 1*0358), 5 C.C. phosphoric acid, and diluted with water to 150 C.C. A current liberating 0% C.C. OH gas per minute acted upon the solution for a period of ten hours. The precipated platinum metal wm quite adherent. It weighed 0.1140 gram.The calculated amount of platinum corresponding to the quantity of double salt used in the trial is 0.1144 gram. The error is therefore 0.0004 gram. Two additional trials gave 0.1255 gram. and 0.1263 gram. metal. The required quantity of platinum was 0.1260 gram. The filtrates from these deposits were not discoloured upon the addition of hydrogen sulphide. The precipitated metal was deposited upon a copper-coated platinum surface. A current best suited for the precipitation of 0*1-0*2 gram. metallic platinum should give about 0.4 C.C. oxyhydrogen gas per minute, If the current exceeds 0*7-0*8 c.c, OH i t was wasbed with water and alcohol.THE ANALYST. 97 gas per minute, the platinum i R apt to separate in a spongy condition, and when the current falls at low as 0.2 C.C. OH gas per minute, the copper coating dissolves.Platinum is deposited very rapidly from its acid phosphate solution by the current. The conditions outlined above allow of the electrolytic separation of platinum from the metals of the third and fourth groups. Pa Zladizcm . This metal, under the influence of the current, separates very rapidly from a solution containing free phosphoric acid. The deposition is also complete. 1. A solution containing 0.1825 gram. palladium, 20 C.C. disodium phosphate (sp. gr., 1.0358), 5 C.C. phosphoric add (sp. gr., 1*347), and 125 C.C. of water was electrolysed with a current giving 0.7 C.C. OH gas per minute. The deposited metal weighed 0.1817 gram. The deposition was made upon a copper-coated platinum dish.2. The conditions of experiment were analogous t Q those in 1. The precipitated platinum weighed 0.1830 gram. In each instance the deposit of metal was compact and adherent. It resembled ordinary sheet palladium in appearance after it was dried. The efforts made to separate palladium from cadmium, zinc and other metals were fruitless. The palladium was always fully precipitated, but it either carried down with it as much as 3 per cent. of the associated metal, or it separated in spongy, black masses. For the present the acid phosphate solution of palladium can only be recommended for electrolysis when other metals aro not present with the palladium. Cold. It was washed with hot water. 1. The solution contained 0.1338 gram. gold, 20 C.C. disodium phosphate (ap.p,, 1*038), and 3 C.C. phosphoric acid (sp. gr., 1.347). Current, 0.8 C.C. OH gas per minute. The deposit weighed 0.1335 gram. The metallic deposit was quite adherent and compact. It was washed with hot water. 2. The conditions were similar t o those just mentioned under 1. The gold deposit weighed 0.1339 gram, Trials made for the purpose of separating gold from cadmium were not successful. The same behaviour was observed here as with palladium and cadmium. The gold separated compieteiy from the solution, but it either carried down cadmium or it separated in a spongy mass. This last occurrence was always noticed when the quantity of phosphoric acid was increased. I failed to separate palladium from zinc, notwithstanding the conditions were re- peatedly modified.With gold and zinc the separation proceeded without the least difficulty. Gold from Ziw. A solution of 150 C.C. volume contained 0.1338 gram. gold, 0.1500 gram. zinc, 30 It was electrolysed The gold deposit was compact, and It weighed Total dilution, 160 C.C. The metal was deposited.upon copper. The filtrate mas found free from gold. C.C. disodium phosphate (sp. gr., 1*0358), and 3 C.C. phosphoric acid. with a current giving 016 C.C. OH gas per minute. readily washed with hot water. 0.1338 gram, It was dried over a warm iron plate. Zinc was not precipitated.9s TRE AXALYST. Gold from Co6alt. The quantity of metallic gold present was the tame a8 in the preceding separation. The metallic cobalt was 0*2300 gram. The conditions, in all other respects, were the same as in the separation of gold from zinc. The precipitated gold weighed 00133s gram. The current employed in the experiments recorded in this communication was derived from the ‘‘ crowfoot ” cells of the ordinary form. The flat platinum spiral in connection with the anode of the battery was 12 inches from the cathode dish, in which the depositions of metal were made. All the procipitations occuzred at the ordinary temperature. The electrolysis of zinc, nickel, cob& and iron phosphates, in acid solution, has thus far not yielded very encouraging results. Eveu then the deposition of the metals is rather slow. Strong currents seem necessary.

ISSN:0003-2654    

DOI:10.1039/AN8911600095

出版商:RSC    

年代:1891

数据来源: RSC

摘要:

9s TRE AXALYST. REPORT OF RECENT RESEARCHES AND INPROVEM-ENTS I N ANALYTICAL PROCESSES. NEW METHOD FOR THE ANALYSIS OF PEPTONES. BY A. DENAEYER, BRUSSELS (Bulletin de E’Association BeZp des Chimistes, 1st Dee., 1890). The author has modified the method previously described by him (THE ANALYST, June, 1890), further researches having shown that it was in several respects capable of improvement. During the peptic digestion of meat the gelatine of the connective tissue undergoes a more or less complete chemical change. When the action of acid pepsine at a temperature o€ 40°-450C. is carried to its extreme limit, the whole of the gelatine is transformed into an allotropic, non-jellifiable variety which is soluble in alcohol, h ordinary peptones both kinds of gelatine are commonly present.They contain 15.3 per cent. nitrogen, whereas albumose and peptone only contain 17 per cent., and as they are not originally assimilable, it is evident that any analysis in which they are confounded with true peptone is of little value. 1. A carefully filtered solution of 2 grams. of dry peptono in 10 grams. of water is treated with 90 grams. alcohol of 90°. After standing for twenty-four hours the pre- cipitate is washed with alcohol. It consists of albumen, albumose, peptone, and normal jellifiable gelatine. I n its present form the method is as follows :- The filtrate is reserved for process 6. 2. poor aibwmen. m. The above precipitate is digested with hof water, and washed on a tared filter. The residue is dried and weighed ~ n 4 albumen, which was rendered insoluble by the alcohol.3. Yoor norma2 gelatine. The filtrate from albumen is treated with excess of neutral eolution of mercuric chloride (instead of double iodide of mercury and potassium as formerly). The solution containing HgCI, is now treated in a tared beaker with excess of ammonium sulphate in crystals, boiled and cooled. Gelatine adheres to the beaker and may be washed with (NH,), SO,, dried and weighed. It is then digsolved in hot water diluted to 100 c.c., the ammonium sulphate estimated by standard barium chloride, and its weight; deducted from the gelatine, This throws down albumose and peptone, but not gelatine. Ppt. rejected,THE ANALYST. 99 4. For albzcrnose. A fresh portion is treated successively with alcohol and water, as in ‘1 and 2.The aqueous solution of albumose, peptone, and gelatine is treated as before, with excess of (NH,), SO,. This throws down albumose and gelatine, but not peptone. The precipitate is collected partly on a tared filter, and partly in a tared beaker. After washing with (NHJ, SO,, the sulphate is estimated and deducted as before, Then the gelatine being known, albumose is found by differenae. 5. Foypeptona. An aqueous solution of albumose, peptone, and gelatine is prepared as before. This is treated with excess of solution of phosphotungstate of soda, prepared as follows :-Tungstate of soda, 50 grams. ; boiling distilled water, 1,000 grams. ; phosphoric acid, 100 grams.; hydrochloric acid, 150 grams. ; acid added after cooled, and solution filtered after twenty-four hours.This reagent throws down all three of the nitrogenous compounds. After settlement and partial decantation the precipitate is thrown on a tared Schloicher’s filter, washed with dilute hydrochloric acid, dried and weighed. It is then incinerated, and the weight of the precipitate-minus the ash- gives the three ingredients, and, of course, the peptone by difference. The alcoholic solution (1) is divided into two portions, One of these is evaporated, the residue extracted wibh water, and the gelatine estimated as before by means of ammonium sulphate. The other may be evaporated to dryness and weighed, but as the residue is very hydroscopic, it is better to estimate the extractive matters by difference. I n addition to this method of analysis, M. Denaoyer’s paper contains much that is important with regard to the albumens of meat preparations and the processes by which they can be separated; but for further details we must refer to the original paper, a translation of which has recently been published in pamphlet form by Messrs.Straker and Sons, Fenchurch Street, London. 6. For non-jellijnble gelutiiae and extractives. C. W. H. TANNATE OF QUININE. DR. J. E. DE T R Y . (Ned Tydschr v. Pharmncie, etc, April, 1891.)-This compound is supposed to get a dirty colour when thoroughly dried, and the ccmmercial product, therefore, generally contains some water, sometimes as much as 8 per cent. The author, however, found a thorough drying on the water-bath to yield an almost white product. To ascertain its purity the amount of quinine must be estimated as follows : Two grams.of the sample are shaken up in a separating funnel with 16 C.C. of cold water. When thoroughly mixed, 5 C.C. of soda leg are added and 30 C.C. of ether., and the whole well shaken. As ether is somewhat soluble in water, this will retain some ether, and consequently some quinine, which may, however, be completely removed by a second agitation with 30 C.C. of fresh ether. The quinine left on evaporation of the ether is then weighed, but must be further tested as to its purity. The author now makes it into sulphate, and then examines this by his chromate method, a full description of which will be found in the ANALYST, 1889. L. DE K. ON SOURCES OF ERRORS IN THE ESTIMATION OF ZINC BY MEANS OF FERROCYANIDE. DR.F. MOLDENHAUEB. (Chem. Zeit., No. 14, 1891,)-The estimation of zinc by means of ferrocyanide, with copper sulphate paper as indicator, has gradually superseded the time- honoured titration with sodium sulphide. The process, however, like many others, ia occasionally found wanting. The author has studied the influence of the presence of some other metals. Of the alkaline earths and lighter metals, there are only two whose ferrocyanides are quite insoluble in ammonia, viz., zinc and manganese, This magnesia compound is but little soluble. To see if it is possible to titrate zinc when mixed with lime, strontia, alumina, iron, and lead, several mixtures were made, and it seemed quite100 THE ANALYST. possible to get a fair estimation of the zinc in presence of these metals.The presence of such ferric oxide only slightlyinfluenced the result. But it is difforent in the case of magnesia and manganese. Of these bodies a not inconsiderable amount is precipitated by the ferrocyanide, and the amount of zinc may, in consequence, be found from 3 to 6 per cent. too high. After many experiments, the author has now finally adopted the following process :- 2.5 grams, of the ore are dissolved in hydrochloric acid, oxidised with nitric acid, and, without filtering, diluted up to 250 C.C. 50 C.C. of this solution are put into a flask and mixed with 10 C.C. of ammonia and 5 C.C. of a soolution containing 5 grams, of officinal ammonium carbonate, 5 grams. of ammonium chloride, 10 C.C. of ammonia, and 90 C.C. of water. In the mean- while 25 C.C.of the original solution are mixed with 10 C.C. of ammonia and titratod with ferrooyanide to get an idea how much it takes. Another 25 C.C. may then be titrated more accurately, To the 60 C.C. of the fluid, which has now had time to cool, 2 C.O. of a 10 per oent. solution of sodium phosphate are added. This will cause both the magnesia and manganese to separate out as phosphates. If no separation takes plaue, the titration with the ferrocyanide ought to give the same percentage of zinc as before, but if there should have been Mg. or Xn. the result, although lower than the first, should be taken as the true one. To make the precipitate settle, the liquid is heated. The test analysis is very satisfactory. L. DE I(. ROESE’S PROCESS FOR THE ESTIMATION OF ALCOHOL.R. BENEDIKT (Chem, Zeit., No. 4, ’9l).-Dr. Roese has recommended B process for the estimation of alcohol, based on its complete oxidation to carbonic acid, by means of permanganate. In a tared flask, 5 C.C. of the 1 per cent. solution of alcohol are mixed with 50 C.C. of a 1 per cent. solution of permanganate and then with 20 C.C. of strong sulphuric acid, delivered from a pipette, After a minute, 100 C.C. of water are added, and then an excess of $ solu- tion of potaasium tetra-oxalate ; the liquid heated to boiling and checked back with perman ganate. Although the author worked exactly according to Roese’s directions, he has obtained no satisfactory results. The strength of his solutions was practically the same as of those employed by Roese, 50 C.C. oxaliu solution requiring 15.5 C.C. of permanganate. If 50 C.C. of the premanganate are mixed with even only 10 C.C. of sulphuric acid instead of 20, the permanganate is rapidly decomposed and deposits manganic peroxide. I n presence of spirit, one also obtains a turbid liquid which requires much more oxalate to clear up than Row believes, showing that all the alcohol has not been oxidised. The comparison of the following figures shows the author’s numbers to widely differ from Rowe’s :- Roeee. Benedikt. 1 per cent. alcohol . . 5.002 .. 5.0102 C,H,O . . .. *05002 .. *0591 Permanganate used . . 50 c.c. , . 50 C.C. Checked back with . . 5.6 C.C. . 3.6 C.C. 56.CO 53.60 15.37 Allowance for 50 C.C. of oxslate Reduced by alcohol .. 40.23 . . 27-56 % . -050 . , -034 26.04 (for 84 C.C. of oxalsfe.) -- - - Alcohol E. DE -K,

ISSN:0003-2654    

DOI:10.1039/AN8911600098

出版商:RSC    

年代:1891

数据来源: RSC