摘要:

THE ANALYST. MAY, 1896. PROCEEDINGS OF THE SOCIETY OF PUBLIC ANALYSTS. THE monthly meeting of the Society was held on Wednesday, April 1, 1896, at 8 p.m., in the Chemical Society’s Rooms, Burlington House, the President (Dr. Stevenson) occupying the chair. The minutes of the previous meeting were read and confirmed. The following gentlemen were elected : As members-F. W. Richardson and Walter Thorp, B.Sc. (Lond.). Mr. Rhys Pendrill Charles, F.I.C., F.C.S., Public Analyst for the County of Brecon and the Boroughs of Carmarthen and Neath, was proposed for election as member. The following papera were read : L L The Bacteriological Examination of Water for the Typhoid Bacillus,” by T. H. Pearmain and C. G. Moor, M.A. ; I ‘ Note on the Estimation of Formic Aldehyde,” by Harry M.Smith. The PRESIDENT, in referring to the discussion which had been announced on the subject of the form of certificates, as affected by the recent judgment in the case of Fortune v. Hanson, said that a verbatim copy of this judgment had been obtained, which some members of the Society wished should be read. The Council had ordered the issue of a circular embodying the judgment, and made certain recommendations. He (the President) thought that if the judgment were right, and members would consider the circular and the suggestions which it contained, it might perhaps be better to adjourn any discussion to some future meeting, if such discussion was found to be necessary. Dr. DYEX (Ron. Secretary) then read the notes of the judginent of Mr. Justice Hawkins and Mr. Justice Kennedy in the case of Fortune 2 .Hanson, from ‘L The Law Reports,” 1896, March 2 (vol. i., Q.B., part iii., p. 205), and also the forms of certificate suggested by the Council for the cases of watered milk, and butter cmtaining excess of water, the Council being of opinion that the decision of the court should be regarded as applying only to watered milk and the analogous case of watered butter. The Council had decided to recommend the following forms of certificates : I.-WATERED MILK. L L I am of opinion that the said sample contains the parts as under : Milk ... ... ... Added watel- ... ... ... 100 -00114 THE ANALYST. ” This opinion is based upon the fact that the sample contained only.. . , . . . . . Per cent, of non-fatty solids, whereas normal milk contains at least 8.5 per cent.of non- fatty solids.” 11.-WATERED BUTTER. ‘‘ I am of opinion that the said sample contained the parts as under : Water ... ... ... per cent. “ Genuine butter should not contain more than 16 per cent. of water.” He (Dr. Dyer) observed that Mr. Justice Hawkins had said that the magistrates ought to be informed on the certificate as to the total percentage of water found in the sample. The Council was of opinion--and he thought that anybody carefully reading the judgment would be of opinion-that that might possibly be construed as a figure of speech. What the judge substantially laid down was that the magistrates should have before them the result of the analysis, and the standard upon which the adulteration was calculated, No doubt the judge thought-as a layman would be likely to think-that the water itself was the standard, and therefore he mentioned water.If he had known that the calculation was made upon the non-fatty solids, he would probably have referred to non-fatty solids. The Council felt that the forms of certificate suggested complied absolutely with the spirit of the judgment in question. The circular, while recotninendiag public analysts to adopt the forms of certificate suggested, also recommended them to submit these forms of certificate to the cleiks of their local authorities, as coming from the Council of the Society of Public Analysts. Mr. RAYMOND Ross asked whether it would not be well, in the case of the certificate relating to watered milk, to add the words L‘ not less than” and “not more than !’ to the figures ? Dr.DYER said it seemed to him that this might introduce a little complication, although undoubtedly it would be a inore accurate statement of the analyst’s opinion. Mr. Ross : And perhaps would prevent any dispute as to whether the results of two analysts absolutely and exactly coincided. Dr. DYER observed that such a qualification was virtually implied further on, in the words, “ whereas normal milk contains at least.” This point had not been over- looked, but had been very carefully considered by the Council. Mr. A. E. EKINS said that for some time past he had been in the habit of putting the figures of the analyses of milks in the corner of the certificate. Several defendants had been represented by solicitors, but in no case had they been able to upset the certificate, and he thought the practice could not be regarded as incorrect.The PRESIDENT said he had been in the habit of acting as Mr. Ekins had done, but this did not appear to completely conform to the requirements of the judgment, and the Council had thought it best to frame a certificate or certificates which, so far as they could ascertain, were in accordance with those requirements; and they recommended that every analyst should submit such certificates to the legal advisers of his authority, each analyst being guided, of course, by the opinion of those who advised him in legal matters. More than this the Council could not do.THE ANALYST. 115 Mr. CASSAL said he had great pleasure in rising to propose that the Society should pass a very cordial vote of thanks to their past President, Mr.Hehner, for the admirable evidence which he had recently given before the Food Products Adulteration Committee of the House of Commons on behalf of the Society of Public Analysts (applause). I t would be withiu the recollection of the Society that a strong desire had been expressed that several of the active members of the Society should give evidence before this Committee, and that the Council had appointed three members-Mr. Hehner, Mr. Allen, and himself-to represent the Society. For reasons which at present were not very clear or satisfactory, the chairman of the Committee, Mr. T. W. Russell, somewhat suddenly announced a few days ago that the Committee considered they had received sufficient evidence, and that they proposed to close their inquiry and present their report.Very fortunately for the interests of the country, and very fortunately for everybody who held the position of Public Analyst in Great Britain and Ireland, Mr. Hehner had been heard, and he would strongly recorninend every member of the Society who took an interest in the scientific and official work of Public Analysts to carefully read the evidence which Mr. Hehner had given on their behalf. It was the result, as he (Mr. Cassal) had reafion to know, not only of very arduous and painstaking work, but of constant attendance, often at great personal inconvenience, at the meetings of the Food Products Committee, where one had to sit and listen to a good deal of what it would not be improper to call dreadful nonsense, to many ignorant or misleading statements, and, in fact, to much which could not but be extremely irritating to any member of that Society.The questions that had to be dealt with were, as the Society knew, extremely complicated; and in view of the fact that some members of the Committee were decidedly hostile to the position which had been taken up by the Society of Public Analysts, Mr. Hehner’s work was rendered all the more difficult. I n the result, Mr. Hehner had proved himself a most worthy representative of the Society (hear, hear), and his evidence was admirable from beginning to end. There was one point touched upon which, as it was a matter of great importance, he might be pardoned for referring to.A question was put to Mr. Hehner as to what were the qualifica- tions for admission to the Society of Public Analysts, and as to what steps, if any, were taken to ensure the restriction of membership of the Society to properly-qualified persons. I t was hardly possible to explain to the Committee that the Society’s system of proposal and election, properly applied-as it had been, at any rate, during recent years--was sufficient to ensure the exclusion of unqualified men, and that if, by any chance, there should be any such now in the Society, they must be very few. I t was absurdly unjustifiable to draw the conclusion, which one member of the Com- mittee appears to have drawn from Mr. Hehner’s answers, that the Public Analysts as a body were not qualified to advise the Committee, or to put forward some of their number as fitted to sit on a Board of Reference and Control, because the Society’s rules did not make it compulsory on candidates for election to have a scientific degree. He (Mr.Cassal) mentioned this matter because he felt that it was the duty of every member of the Society to see that no person was elected as a member of whom they would afterwards have reason to be ashamed; and he trusted that every member of the Society would be impressed with the full significance of116 THE ANALYST. the question put to Mr. Hehner upon this matter, and with the great importance of always being able to answer such questions as Mr. Hehner had done, or in such a way that the position of the Society before the public should in no degree be weakened.He would just add-and he was sure that Mr. Hehner would bear out the statement-that as a Society they were also very greatly indebted to a member of the Committee who had done most excellent work during its sittings, and who would be found to have rendered a considerable public service by his attention to the matter. He begged to move that the Society should thank Mr. Hehner for the great trouble that he had taken in pre- paring the evidence that he had placed before the Parliamentary committee, and for the admirable way in which he had given that evidence on their behalf (applause). Mr. ALLEN said he rose to second that motion with the very greatest pleasure. At some personal inconvenience, he had attended a number of the meetings of the Parliamentary Committee during the previous sessions.He did not hear Mr. Hehner give his evidence, but he had read every word of it on the proof. H e thought the Society was indebted to Mr. Hehner in the highest degree for the masterly manner in which he had put their case before the Committee, and had met all the cross- questions and difficulties which constantly arose. They might congratulate them- selves on having had their case laid before the Committee in the best possible way, and in a, manner so complete as to leave very little else to be said. Of course, they regretted the premature termination of the Committee’s labours. There were several points which not only Public Analysts, but others interested in the Food Acts, would have been glad to have brought before the Committee; but so far as the Society of Public Analysts were concerned, their case had been stated well, and they had no reason whatever to be dissatisfied with the impression made upon the Committee by Mr.Hehner’s evidence. He had great pleasure in seconding the motion which Mr. Cassal had proposed. The PRESIDENT said that, before putting the motion to the meeting, he would like to add his own word of grateful thanks to Mr. Hehner for the way in which he had attended the meetings of the Select Committee, and for the very able and admirable manner in which he had put the case of the Public Analysts before the Committee. He (the President) had read and re-read the evidence of Mr. Hehner, and the evidence of other analysts, and was quite sure that they had every reason to be very proud of Mr.Hehner, and he was sure that a deep impression had been made upon the Committee by him, The Council of the Society of Public Analysts had already passed a vote of thanks, and of their grateful appreciation of Mr. Hehner’s services. He was sure that a similar vote would be passed at the present meeting with acclamation. He referred to Mr. Hudson E. Kearley, M.P. The resolution was carried unanimously, amid great applause. Mr. HEHNER said that if he had known what was coming he would probably not have been present. He was very deeply grateful for the very kind manner in which the motion had been brought forward and carried. He did not require, how- ever, any vote of thanks. He had identified himself with the Society for many years, and had spent so much thought and work upon it, that to break a lance for the Society had been a labour of love. He sincerely hoped that the views of theTHE ANALYST. 117 Society, as represented by him, had made some impression upon the Committee. He desired to utilize this opportunity, instead of simply rising to thank the meeting, to give those members who were not at the meetings and had not had the recent reports of this Committee a summary of what passed, both as regards his own evidence end the reply to it by Mr. Bannister. Mr. Hehner then gave a sketch of the evidence which he had recently given before the Select Committee of the House of Commons on Food Products Adulteration, and also of the evidence given by Mr. Bannister by way of rejoinder. [A summary of both will be published in the ANALYST hereafter.-E~.]

ISSN:0003-2654    

DOI:10.1039/AN8962100113

出版商:RSC    

年代:1896

数据来源: RSC

摘要:

THE ANALYST. 117 THE BACTERIOLOGICAL EXAMINATION OF WATER FOR THE TYPHOID BACILLUS. BY T. H. PEARMAIN AND C. G. MOOR, M.A. (Read at the Meeting, April 1, 1896.) IT is now universally acknowledged that polluted water is the most important agent in the conveyance of enteric fever. Although water contaminated with sewage has been, and is still, drunk by a large number of people with impunity, so far as the appearance of enteric fever is concerned, yet the slightest contamination of a water- supply with the dejecta from a case of typhoid fever, has, in many well-authenticated instances, caused widespread epidemics of the disease amongst those persons who had used the polluted water-supply. In many of the recorded cases of water-borne typhoid, the amount of organic matter accompanying the specific pollution was so extremely small that the water- supplies have been repeatedly pronounced from the results of chemical analysis to be of high organic purity.Moreover, it has been shown that the organism which is the cause of enteric fever, may, when introduced into potable water of good quality, not only retain its vitality for a considerable period of time, but may multiply almost indefinitely. Therefore the slightest contamination with the alvine discharges from a case of true enteric fever may serve to render dangerous millions of gallons of drinking water. Thus it will be seen that the virulence of typhoid contaminated water is not necessarily dependent upon the organic impurity of the water, but upon the specific pollution. If this is granted, and experimental prooil may be easily applied," it will be admitted that under certain circumstances the question may arise, Has the epidemic of enteric fever now in progress in a given community had its origin in the water-supply? If this question be asked us, as analysts, we see that it is quite conceivable that the chemical analysis of the water by itself may be unable to afford evidence of pollution, owing to the accompanying organic matter being so * A drop of a broth culture of B.typhonw (twenty-four hours old) was well diluted with sterile water. The number of organisms was then estimated by an ordinary gelatin plate culture, when 1 C.C. of the water was found to contain approximately 900,000 organisms. This amount of pollution was not sufficient to raise the amount of albuminoid ammonia appreciably.The tap- water previously contained only 200 organisms per cubic centimetre. 1 C.C. of this diluted' culture was added to 200 C.C. of the ordinary tap-water.118 THE ANALYST, trifling in quantity as to fall below the limits of experimental error. Are we then, to confess total inability to oEer any assistance to discover and remedy the cause of the outbreak? Would not such a course of action as this simply lead to the calling in of others who profess to trust only to the bacteriological examination of water, and deny that the chemical examination has any value? I n short, what we are attempting to show is that every analyst who has to examine potable water should make himself thoroughly acquainted with the latest principles of bacteriological research bearing upon this particular point, so that he may be in a position to himself undertake the search for the specific organism in question with as much confidence in the results of his work as it is possible for one to feel in the present state of our knowledge.number of the epidemics of water-borne typhoid rests on a somewhat incomplete basis, as will be seen from the perusal of an interesting series of papers by Ernest Hart, which have recently appeared in the British Medical Joz~rnal." The bacillus of typhoid fever has, however, been isolated by many competent observers from water that had conveyed and caused the disease. Sonle doubt attaches to the identification of the organism by some of the earlier investigators, owing to the almost constant presence in the waters of other organisms so closely resembling the typhoid bacillus that their differentiation is a matter of great difficulty.The organism which has given rise to much confusion is the I?. coli commzmis. This bacillus is a constant inhabitant of the intestinal tract, and the faeces of both man and animals, and therefore is almost invariably found in all polluted waters. In order to ascertain whether the typhoid bacillus is present in any given water, care must be taken that the B. coli cominunis is not mistaken for the former. This is a very difficult matter, as the vitality of the bacillus coli communis is much greater under all conditions then that of the typhoid bacillus. The object is generally attained by the addition of various chemical substances to the nutrient media, which effectually inhibit or destroy the growth of organisms other than the colon and typhoid bacilli.As pointed out by Frankland, such additions have frequently destroyed the typhoid bacillus, and left the B. coli commzmis, owing to its greater power of resistance, alone master of the field. According to many authorities, notably Messrs. Roux and Rodet, there is reason to believe that the B. coli comrnwzis, under certain conditions, such as growth in sewage, etc., assumes a pathogenic character, and gives rise to a disease which is clinically indistinguishable from enteric fever. This view is borne out to a great extent by the fact that water contaminated with facal matter may be instrumental in causing typhoid fever without the actual access of the specific bacillus, as cases are on record where water long known to be polluted has acquired the property of conveying typhoid without the previous known contamination from a specific case of the disease.This is in accordance with the well-established fact that in places where enteric I t must be admitted that the proof of specific pollution * Water-borne Typhoid-A Historic Summary of the outbreaks in Great Britain and Ireland, 1858 to 1593. By Ernest Hart, British Medical Jozimaf, June 15th, 22nd, 29th; July 6th, 13th, 20th; August 17th, 1895.TRE ANALYST. 119 fever was once endemic, it has disappeared upon the substitution of a pure for a contaminated water supply. Messrs. Deniel and Orlandi" show that Roux and Rodet's statements as to the near relationship of the B.typhosus and the B. coli comnzzsnis are borne out by the physiological and pathological properties of the metabolic products of the two organisms. Animals rendered immune to one are also rendered immune to the other bacillus, the virus of the I?. coli comnzzuzis having a higher therapeutic value than that of the B. typhoszbs. German0 and Maurea,i after a very prolonged investigation, have isolated no less than thirty varieties of tgphoid-like bacilli, and they consider this fact supports the theory that the B. coli commzmis may, under certain conditions, develop into the B. typhosus. Nicolle,: after a very careful investigation, could only find the B. coli comrnuizis in a typical case of enteric fever, the blood and spleen being particularly examined. From the above facts it will be seen that the possible dangers to be derived from the drinking of sewage-polluted waters are enorniously increased.It is worth recording, however, in connection with the above, that Chantemesse has called attention to the fact that during the typhoid epidemic in Paris, in 1894, the soldiers who drank the polluted water supplied to the Mdnilmontant barracks all escaped typhoid, notwithstanding the fact that the water was swarming with the colon bacillus. Dr. Klein has recently studied$ the B. typhosus and B. coli communis as to their stability as separate species in culture, and in the process of transference from animal to animal. On the one hand bacilli of both kinds derived in each instance from human sources, were tested by him as to their vitality, and as to the retention of their differential characters in waters of different composition and quality.He also took the two organisms derived from sources outside the human body, namely from excrementally-polluted water supplies ; these were passed from sub-culture to sub-culture, and were passed from peritoneuni to peritoneum in separate series of guinea-pigs, they being cultured through no less than thirty generations. Whatever the source of the bacilli, and whatever the experimental conditions in the laboratory, or the animal body to which they were exposed, each organism retained unimpaired its differential characters, and at no time did they show the least tendency to depart from the characters generally accepted as being exhibited by these organisms.Incidentally, during the course of these experiments, it appeared that the persistence in a water medium of both the typhoid bacillus and the bacillus coli is largely governed by the chemical constitution of the water. Dr. Elsner, of Berlin, has recently found the B. typhosz~s in the stools of a male nurse in perfect health who attended typhoid patients. The fact that a man in good health can carry the bacillus of enteric fever in his intestines, and thus * Centralb. fiir Bnkterioloyie, xvi., p. 246. t Centralb. Jiir Bakteriologie, xv., p. 60. $ Annales de 1111i,vtit7it Pasteur, 1895, No. 1. $ The 23rd dnirual Report of thr Local t:ovwnmcirl Board-Supplement containing the Report of the Medical Officer, p.459.120 THE ANALYST. disseminate it, throws much light upon the so-called ‘‘ spontaneous ” origin of typhoid fever. The bacillus of typhoid, or enteric, fever (B. typhi abdominalis) was first described by Eberth in the year 1883, who stained it in sections of the intestines of patients who had died of typhoid ; in the following year, Gaffky obtained pure cultures of the organism, which is now known as the Eberth-Gaffky bacillus, The bacillus is 2.5 to 4.0 The Eberth-Gaffky bacillus is not killed by drying, nor by exposure to a low temperature. Its thermal death-point is 55” C., and, according to most observers, it does not form spores. Like all the pathogenic organisms, it is prejudicially aflected by light, diffused daylight being sufficient to prevent its development, while direct sunlight is fatal in five hours. The organism grows equally well both under aerobic and anaerobic conditions.The microscopical appearance alone is not enough to distinguish it from several other organisms-in fact, it is not uncommon to find some stained specimens which have a curved appearance exactly like the “Koch’s Comma,” or the Finkler-Prior bacillus. If a fragment of a recent culture is rubbed up with a droplet of water and examined with a twelfth-inch objective, the bacilli will be seen in active movement, this motility being due to the great number of hair- like flagella by which the organism is covered. The typhoid bacillus stains well with all the usual basic aniline dyes, but is decolorized by Grams’ method of staining. The true Eberth-Gaffky bacillus is readily distinguished from all others by its characteristic growth on the various culture media.Repeated sub-culture, as in the case of many other organisms, produces longer and abnormal forms. Very lengthened forms of the bacillus, which are somewhat characteristic, are sometimes seen in cover-glass preparations ; the long bacilli are known as “ leptothrix ” forms. The Bacillus coZi co?nmziizis is slightly shorter than the typhoid bacillus, and, like it, owes its power of motion to flagella, but it never possesses the profusion of these usually seen in the case of the Eberth-Gaffky bacillus. The following table shows the main points of difference between the typhoid bacillus and the colon bacillus for which it might be mistaken : long by 0.5 ,u thick.Media. Bacillus typhosus. I Bacillus coli communis. I Gelatin plates . The colonies on the surface form large grayish-white ex- pansions with irregular edges, and after a time become somewhat yellowish-brown. The depth colonies are darker, with regular edges. Under a low power the colonies exhibit a character- istic woven structure. The gelatin is not liquefied. The colonies are round and oval, with smooth-rimmed m a r g i n s . The surface- colonies form dirty - white expansions, which, on magni- fication, exhibit a furrowed appearance. The colonies later become dirty yellowish- brown in colour. The gela- tin is not liquefied.THE ANALYST. 121 Media. Gelatin I ' streak " culture ... ... Gelatin '* shake " culture ...... Agar-agar " streak " culture ... ... Potatoes ... ... Milk . . . ... Broth ... ... Formalin b r o t h (1 : 7,000) ... Bacillus typhosus. 'roduces a grayish-white ex- pansion with irregular edges. The growth has a tendency to keep to the inoculation streak, and often has a bluish iridescence. No gas bubbles. Grayish - white expansion, which covers the surface of the medium. Generally a faint grayish- white growth ; the growth varies, however, on different potatoes. Turns faintly acid. No coagu- lation takes place. Rendered turbid, and gives no indol reaction. No growth. Bacillue coli communis. Dirty yellowish white expan- sion, which spreads all over the surface of the media, and often has a bluish iri- descence when viewed by transmitted light. Copious gas formation.Dirty yellowish-white expan- sion, which spreads over the surface of the medium. Slimy yellowish growth. Curdled after one to three days. Rendered turbid, and gives a well - marked indol reaction after from twenty-four to forty-eight hours. Growth. The growths make their appearance on the gelatin media at room temperature after from. forty-eight to sixty hours. The agar-agar, potato, milk, and broth tubes are incubated at 37" C. (blood-heat) for three days. From the above table it is seen that the B. co7i C O I ~ ~ Z L I Z ~ ~ is readily dis- tinguished from the B. tgphoszrs by its cultural characteristics, and particularly by its cheiiiical reactions. The colon bacillus invariably grows more rapidly than the typhoid bacillus. The colon bacillus when grown in alkaline peptone broth produces a red colora- tion on the addition of nitrous acid, depending upon the interaction of nitrous acid with indol, which is one of the products of the metabolism of the organism, to form nitro-indol, which is of a red colour.This test is best applied as follows : To 10 C.C. of the culture of the organism under examination, which has been incubated at blood- heat for not less than twenty-four hours, is added 1 C.C. of a 0.02 per cent. solution of sodium nitrite, and then a few drops of pure concentrated sulphuric acid. If indol is present, a rose to deep red coloration is produced. The foregoing reaction, together with the power of the 13. coli conimuuis of coagulating milk and the formation of gas in nutrient gelatin, provide an easy method of distinguishing this organism from the R.typhosus. When an organism which fails to coagulate milk is isolated from water by any of the methods hereafter given, and does not give rise to gas formation in a gelatin '' shake" culture, and does not cause liquefaction of the gelatin in a122 THE ANALYST. (' streak " culture, and, moreover, yields a negative indol reaction, and, again, has the Bame morphological characters as the B. typhosus, it is at least indistinguishable from the Eberth-Gaffky bacillus, and may with every probability be regarded a s identical with it, Animals do not suffer from enteric fever in the manner in which we know it in man, hence inoculation experiments do not give us any assistance in proving a given organism to be identical with the specific bacillus of typhoid fever. Dr.Klein* has recently pointed out that, although the Eberth-Gaffky bacillus i s regarded as the essential cause of enteric fever, it has never yet been experimentally proved capable of inducing that disease. Rodents inoculated, whether subcutaneously or intra-peritoneally, with this bacillus do indeed suffer fatal illness ; but the malady thus induced is not of a specific nature, and, moreover, may just as easily be pro- duced by the injection of various other microbes. He has shown that the Eberth- Gaffky bacillus may grow and multiply within the inguinal lymph glands of calves. A number of organisms have been described by Cassedebat, Babes, Booker, Klein, Springthorpe, and others, which were obtained from cases which were clinically identical with enteric fever and other sources which resembled the Eberth- Gaffky bacillus, but were shown to present slight but constant differences in their cultural characters. They are only to be differentiated from the true typhoid bacillus by a very careful comparison of cultures made side by side on various media. Casse- debat found three species of these so-called " pseudo-typhoid " bacilli i n the Marseilles water-supply during the great typhoid epidemic in that town during 1891. They all corresponded with the Eberth-Gaffky bacillus in their growth upon gelatin, potato, etc., and they all gave a negative indol reaction. Like the typhoid bacillus, they grew in milk without causing the coagulation of the caseine, but two of them produced an alkaline reaction in this medium, while the third corresponded with the Eberth-Gaff ky bacillus in producing a decided acid reaction. I t does not seem inipossible that these pseudo-typhoid organisms may be the colon bacillus in transition stages. (To be co?zti?zmd.)

ISSN:0003-2654    

DOI:10.1039/AN8962100117

出版商:RSC    

年代:1896

数据来源: RSC

摘要:

122 THE ANALYST. THE ESTIMATION OF THE DIASTATIC POWER O F MALT, ETC. BY W. J. SYKES, M.D., AND C. A. MITCHELL, B.A. (Read a t the Meeting, March 4 , 1896.) AMONGST the different items which have to be ascertained in the examination of malt, the determination of its diastatic power is one of considerable importance, since the requirements of manufacturers in this direction vary considerably, according to the nature of the article they wish to produce. Regarded from a diastatic point of view, malts may roughly be divided into four classes, in a gradually descending scale : Green MaZt.-This is barley fully germinated, and ready for placing on the drying-kiln. Since malt invariably suffers a loss of diastatic power during the drying process, however carefully and in whatever way this may be conducted, some * See the 22nd and 23rd Annual Reports of the Local C7'overnmeizt Board-Supplement containing the Report of the Medical Officer.THE ANALYST.123 distillers, in order to avoid this loss, make use of malt in this form. By doing so they not only avail themselves of malt possessing the highest possible diastatic power, but at the same time save the cost of drying. Air-dried TIalt.-This is green malt dried at the ordinary temperature in a current of air, It is mostly used for experimental purposes, such as the preparation of diastase, etc. Distillers' Malt.-In this the germination of the barley is pushed so far as to develop the diastatic power of the grain to its maximum degree. The green malt so produced is then dried slowly and carefully on the kiln, where it is never allowed to reach a teniperature higher than 120" to 125" F.In this way loss of diastatic power is reduced to the minimum consistent with the production of a staple article. Brewers' Aldt.--In this the germiliation is not carried so far as in the before- mentioned malts, consequently the diastatic power is not developed to the fullest extent. Though in the initial stages of the drying process the heat is applied very slowly and gradually, towards its termination the temperature is allowed t o rise, for pale malts, to 180" F., and for high-dried malts to as much as 210" to 220" F. The malt in these latter stages undergoes a sort of cooking process, which largely develops its flavour and aroma. During this portion of the drying much of its diastatic power is lost, but with malts intended for the brewing of beer, it is necessary that such should be the case.From time to time various processes have been proposed for the estimation of the diastatic power of malt, many of which are of a more or less crude and unsatisfactory nature. The first really efficient process was that devised by Kjeldahl (Comptes rendzu des Travaux de Carlsberg Lab., 1879). I n a series of investigations on the action of diastase on starch, he had discovered that in such transformations the amount of reducing substance formed was strictly proportional to the amount of diastase, so long as the amount produced in the mixture was not allowed to exceed 45 per cent. of the total possible yield. I n other words, to comply with what is now known as 'I Kjeldahl's law of proportionality," the diastase must not be present in a quantity greater than will convert a little less than half the starch present.For the actual determination, 10 grammes of the malt, after being finely ground, were extracted with 400 C.C. of water for six hours; 15 C.C. of the bright filtrate from this were added to 200" C.C. of a 3 to 4 per cent, solution of soluble starch, heated to a temperature of from 57" to 59" C., at which temperature the whole was kept for twenty minutes. The amount of reducing substance reckoned as maltose was then determined either gravinietrically, volumetrically, or colorinietrically, and from this the amount of reducing substance contained in the original soluble starch solution was deducted.The diastatic power was considered to equal 100, when 15 C.C. of malt- extract of the above strength and under the above conditions yielded an increase of cuprous oxide equivalent to 1 gramnie of maltose, The soluble starch used in Kjel- dahl's process was prepared by allowing an aqueous extract of malt to act upon gela- tinized starch at a high temperature (180" F.). I n such a case, those portions of the diastase, which convert the starch into bodies capable of reducing Fehling's solution, are almost completely destroyed, and only the liquefying portion of the diastase remains intact-that is, the portion which converts gelatinized starch into its soluble124 THE ANALYST. modification. However carefully the operation may be performed, some reducing bodies are invariably produced, hence it is necessary to determine their amount in each fresh batch of solution employed ; and as soluble starch solution is unstable, it must be prepared as wanted, and this is a distinct inconvenience.Some ten years later C. J. Lintner discovered that soluble starch could be readily prepared in a stable form by the limited action of various acids upon starch, a fact which he practically applied to the simplification of Kjeldahl's process. Lintner's soluble starch is prepared by allowing potato starch to stand under 7.5 per cent. hydrochloric acid for seven days a t the ordinary temperature, or for three days at a, temperature of 104" F. The same result can be obtained, according to Brown and Morris (Trans. Chem. Soc., 1889, p.450), in twenty-four hours, at the ordinary temperature, by employing 12 per cent. hydrochloric acid. The starch is then washed until free from acid, dried in the air, and preserved for use. Under this treatment the starch completely loses its power of forming a paste ; and though it is almost insoluble in cold water, is readily soluble in that medium at temperatures over 60" or 70" C., from which it again very slowly separates on cooling. On microscopic examination no change can be detected in the appearance of the starch granules either with ordinary or with polarized light. Its solution has not the slightest reducing action upon Fehling's solution. For the estimation of the diastatic power of a substance, a 2 per cent. solution of this soluble starch is employed.It is best prepared by placing the required amount of water in a flask, and the weighed quantity of soluble .starch in a smaller beaker. Sufficient water is poured from the flask on to the soluble starch to form a mixture of the consistence of thick cream, the remainder of the water in the flask brought to near its boiling point, and the well-stirred contents of the beaker poured in, when the soluble starch dissolves immediately. A little of the hot solution is poured into the beaker to dissolve any remnants of starch, and returned to the contents of the flask, which are then allowed to cool. Twenty-five grammes of malt are finely ground in a coffee-mill and stirred into 500 C.C. of water. The mixture is allowed to stand for six hours, with an occasional stir.The solution is filtered through a dry filter-paper, the first cloudy portions rejected, and about 50 C.C. of the bright filtrate (malt-extract) collected. Ten test-tubes, of a capacity of about 20 c.c., are taken, and 10 C.C. of the cold 2 per cent. soluble starch solution pipetted into each. To the first of these is added 0.1 C.C. of the malt-extract, to the second 0.2 c.c., and so on, so that the tenth test- tube receives 1.0 C.C. After each tube has been well shaken, the whole are allowed to stand for one hour in a water-bath kept at a temperature of 70" F. At the expiration of this period, 5 C.C. of Fehling's solution are added to each, the tubes well shaken, and immersed in boiling water for twenty minutes, after which they are taken out and examined.It will perhaps be found that the contents of one of the tubes are colorless, in which case the amount of malt-extract added to this tube is taken for the subsequent calculation. Oftener the contents of one tube are yellow, the next one blue ; in this case the average of the amounts added to the two tubes is taken. The diastatic power is calculated on the basis that when 0.1 C.C. of malt-extractTHE ANALYST. 125 of the above strength added to 10 C.C. of 2 per cent. soluble starch solution, and treated in the above manner, yields just sufficient reducing substance to exactly reduce 5 C.C. of Fehling’s solution, the diastatic power of the malt yielding the extract shall be taken as 100. The diastatic power of any other malt is found by a sum in inverse proportion.For instance, if in such a determination the end point is found to lie between the sixth and seventh tube, the amount of malt-extract to be taken would be 0.6 + 0 . 7 ~ 2 = 0.65, and o.65 x 0.1 = 15.55. This figure must then be cal- culated upon water-free malt : supposing the malt contained 4.5 per cent. of moisture, then ::\ x 15.55 = 16.23 expresses the diastatic power of the malt on Lintner’s scale. I n the examination of green malts, where the diastatic power often exceeds 100, the malt-extract is diluted with an equal volume of water before being added to the soluble starch tubes. For determining the diastatic power of precipitated diastase, a solution of 0.03 grammes of the substance in 25 C.C. of water takes the place of the malt extract. Consequently, the energy of a precipitated diastase is considered as 100 when 0.12 milligramme yields just sufficient reducing substance to decolorize 5 C.C. of Fehling’s solution under the above experimental conditions.This quantity was fixed upon because it represented the power of the most energetic diastase which had been then obtained. In recent times Osborne (ANALYST, xx. 232) has prepared a diastase six hundred times as energetic as this. I n examining such specimens, the diastase solution has to be made correspondingly weaker ; the right proportion is found by preparatory trials of soIutions of various Rtrengths, in which 0.1 and 1.0 of the solution are respectively added to 10 C.C. soluble starch solu- tion. When one of these after treatment with Fehling’s solution shows over, and the other under, reduction, the solution of diastase is of the proper strength.The degree of dilution must obviously be taken into account in the subsequent calculation. For conducting experiments of this kind, the star-apparatus of Reischauer, illustrated in the accompanying engraving, is exceedingly convenient A special pipette, graduated so as to deliver quan tities gradually increasing from 0.1 C.C. to 1.0 C.C. by 0.1 c.c., is also useful, I t is obvious that in the above method there are only ten definitely fixed points, and consequently a definite result can only be obtained in the opera- tion when oiie of the tubes is exactly decolorized, and this rarely happens in practice. Should the end point lie between two tubes, in order to obtain a more approximate result the operation must be repeated with gradually increasing quantities of malt-extract, commencing with the quantity which caused incomplete reduction, 100 The result is then multiplied by 2.126 THE ANALYST. and ending with that which produced over-reduction, Should the end-point again fall between two tubes, the operation has to be performed a third time, and so on.I n the determination of the diastatic power of brewers' malts, which range from 25 to 45, since the end-point does not fall between the first and second tube, the numbers found are, as a rule, sufficiently approximate for practical purposes, and in any case do not require more than one repetition of the operation. With distillers' malts the case is different ; the end-point generally falls between the first and second tube, and between these there is a wide gap-from 50 to 100.I n order to avoid several repetitions of the operation, and to obtain the desired result in one determination, we suggest a slight modification, which to some extent combines the methods of Kjeldahl and Lintner. The soluble starch solution, malt- extract, and diastase solution, are all prepared in the manner mentioned before. Instead, however, of employing a number of tubes, we make use of one small wide- mouthed flask, of a capacity of about 200 C.C. Into this I00 C.C. of the soluble starch solution are placed, 1.0 C.C. of the malt-extract added, the whole well shaken, and allowed to stand at a temperature of 70" F. for one hour ; 50 C.C. of Fehling's solution are then added, the flask, with its mouth covered with a watch-glass,* placed on wire- gauze over a Bunsen-flame, and heated up to 98" C.I t is then removed from the flame, and immersed in boiling water for seven minutes. It has been found experimentally that by proceeding in this way the contents of the flask are submitted to conditions of temperature and time closely approximating those of the test-tubes employed in Lintner's method. The cuprous oxide is collected in a, Soxhlet filter- tube, redaced in hydrogen, and weighed. The weight of the copper found, divided by 0.438 (the quantity of copper contained in 50 C.C. of Fehling's solution), and multiplied by 100, gives the diastatic power. I n this way a determinate figure is obtained for any diastatic power between 0 and 100 by one operation.I n the following table we give the results of a nuniber of experiments which were made with a view to determining how the figures obtained in this way agree with those obtained by Lintner's method : Uiastatic Power. Moisture Extract L i n w s and Malt. per cent. lbs. per quarter. Method. Mitchell. Remarks, 1. English ... ... - - 5 3.3 Old musty sample. 2. Smyrna (Black 3. Foreign ... ... 3.8 85-34 12 15 4. Syrian ... ... 6-7 78.96 12 15.7 5. English ... ... 12-7 - 17 22 Old sample. 6. Syrian ... ... 4.01 85 SO 19 22.7 7. English ... 4.17 90.72 21 22.8 Said to be low dried. 8. Yorkshire (1892)' 10.1 I 25 24 9. Foreign ... ... 7.3 77 40 38.7 10. English ... ... 4.7 94 77.2 83 Dried at 125" to and White, 1892) - - 10 11.2 130" Fahr.* Bearing in mind Kjeldahl's experiments (ANALYST, xx. 227), in some cases a current of hydrogen was passed through the flask during the heating process, in others the flask was simply covered with a watch-glass. This latter precaution was found sufficient to prevent the disturbing influence of the atmospheric oxygen.THE ANALYST. 127 The time required for making an estimation, amounting to about eight hours in all, is often a very inconvenient one ; but we have found that the malt-extract may be filtered after the six hours, and the filtrate left until the next day without affecting the result. This is shown by the results given in the following table : Estimation immediately after filtering. Estimation next day. Sample. Lintner’s. S. and M.Lintner’s. S. and M. 3 ... 12 ... 15 ... 14 ... 16 5 ... 17 ... 22 ... 16 ... 18 6 ... 19 ... 22.7 ... 19 ... _” From these examples it will be seen that the figures obtained by our method agree fairly well with those obtained by Lintner’s. I t is probable that the Eormer are the more accurate, since under the conditions of the process Kjeldahl’s law of proportionality is strictly adhered to, and the figures obtained by Lintner’s method are often the average between two tubes. As the whole process is to a great extent of an empirical nature, the results obtained by either modification would possess the same utility for practical purposes. We can, however, fairly claim that a closer result is obtained in a shorter time by our method, and that it is especially useful when malts having high diastatic powers have to be dealt with.DISCUSSION. Mr. A. R. LING said that he was glad to hear that the authors regarded the method as a purely empirical one, and, in his opinion, it must remain so. I t had been stated by several observers-and his own experiments in conjunction with Mr. J. L. Baker bore out that statement-that when some malts were made to act on starch paste, a certain amount of glucose was found among the products of the trans- formation, and, in the case of these malts, of course, Kjeldahl’s law of proportionality -on which the method of determining diastatic powers was based-would not hold. In the method as usually carried out the diastatic solution (malt extract) was allowed to act on the solution of soluble starch at practically the ordinary temperature.But, inasmuch as the mashing temperature adopted in brewing was considerably above this, he thought that the deterinination of the diastatic capacity of a malt at the particular temperature at which it was to be afterwards mashed would perhaps furnish information of greater practical utility. He had used an ordinary titration iiiethod for determining the diastatic power of malt, and found that it yielded results which compared favourably with those obtained by Lintner’s method With regard to malts of very high diastatic power, in Lintner’s method the value indicated between the first two tubes--containing 0.1 and 0.2 C.C. of malt, extract respectively-was 100 - 50 ; and he should like to know the accuracy which could be attained by the author’s method with malts of this class.Mr. A. C. CHAPMAN asked if the authors could give any information as to the working of the process in connection with distillers’ malts of very high diastatic power, viz., higher than 77, which was the highest mentioned in the table, as he understood that the process had been devised more particularly to meet the requirements of such cases. In the examples given the agreement of the numbers with those obtained by Lintner’s method was certainly good. He also pointed out that if it were permissible to allow the aqueous malt extract to stand overnight in this case, the same might be128 THE ANALYST. said of Lintner’s method, for the experiments were up to this point carried out in practically the same manner in the two methods, The suggested correction for the reducing substances in the aqueous malt extract had always appeared to him to be unnecessary in view of the limits within which it was possible to reach the differences between the various tubes.With regard to the estimation of the amount of copper obtained, he had obtained perfectly satisfactory results by weighing the cuprous oxide direct, which was of course much simpler and quicker than reduction in hydrogen. He used a platinum Gooch’s crucible, and filtered off and washed the oxide with the aid of a filter pump. The time occupied in filtering, washing, drying and weighing, did not amount to many minutes. Dr. SYKES, in reply, said that although the method they had described, as with all other8 on the same principle, could not be said to be an absolute measure of the diastase, still, since Lintner’s figure was usually an estimate between two tubes, he thought the figures they obtained were more determinate. With regard to the reducing bodies formed, he thought it was exceedingly probable that they did vary materially in different cases, but, as the whole subject of the transformation of starch under the action of diastase was still involved in con- siderable obscurity, it was impossible to say what the differences were. Mr. Ling’s proposal to conduct the diastase determinations at the temperature a t which the malt would be used in actual practice, was certainly a point worthy of consideration. It might probably be found that such a course would yield results more in accordance with the behaviour of the malt in the mash-tun. With regard to Mr. Chapman’s inquiry about distillers’ malts, such samples seemed somexhat difficult to meet with, and the figures referred to iu the tables were the highest they had been so far able to obtain. There was no objection to letting the filtered malt extract remain overnight when Lintner’s process was employed. They had estimated the copper by reduction in hydrogen, because the almost universal consensw of opinion appeared to favour the view that this was the most exact method. If no oxidation of the cuprous oxide took place in Mr. Chapman’s method, then, by an alteration of the factor, it would serve equally well.

ISSN:0003-2654    

DOI:10.1039/AN8962100122

出版商:RSC    

年代:1896

数据来源: RSC

摘要:

128 THE ANALYST. OFFICIAL METHODS FOR THE ANALYSIS O F FERTILIZERS, ISSUED BY THE GERMAN MANURE MANUFACTURERS’ ASSOCIATION, HARZBURG, MAY 28, 1895. CONTXIBUTED BY H. H. B. SHEPHERD, F.I.C., ANGLO-CONTINENTAL GUANO WORKS, LONDON. (Continued front p . 101. j 3. The Molybdate Method.-Preparation of the Molybdeitiinz. Solution.*-One hundred grammes of pure molybdic acid are dissolved in 400 grammes of a 10 per cent. solution of ammonia, (0.960 specific gravity), and this solution is mixed while * According to the Berlin reaolutinns of 1)eceniber 14, 1891 ; Halle, 1893.THE ANALYST. 129 shaken with 1,500 grammes nitric acid of 1.2 specific gravity. It is then placed in a water-bath heated to 50" C. for one hour, and afterwards left €or two or three days in a warm place,.to ensure the precipitation of any phosphoric acid that may he present.It is desirable not to allow the temperature to exceed 50" C., as at 90" C. the separation of molybdic acid is very considerable. Preparation of the Magnesia Miztzwe (the Halle formula, containing an increased quantity of ammonia),-Five hundred and fifty grammes magnesium chloride, and 1,050 grammes ammonium chloride, are dissolved in water with 34 litres of con- centrated ammonia (24 per cent. = 0.91 specific gravity), and the mixture made up to 10 litres. Determination.-For materials (superphosphates or raw-phosphates) containing up to 20 per cent. phosphoric acid, 50 C.C. of the solution = 1 gramme substance, are to be taken ; and for materials above 20 per cent. phosphoric acid, 25 C.C.= gramme substance. Two hundred C.C. molybdenum solution are added, and the solution digested on the water-bath for three hours at 50" C. It is then cooled, and the yellow precipitate filtered off through a small funnel, care being taken not to allow more of the precipitate than possible to pass on to the filter. The precipitate is then repeatedly washed by decantation with a mixture of 100 parts of the above-mentioned molybdenum solution, 20 parts nitric acid of 1.2 specific gravity, and 80 parts water, until lime is no longer found in the washings. Five washings with 20 C.C. appear to be sufficient. The test for lime is the appearance or not of turbidity on adding a little alcohol acidified with sulphuric acid to 1 C.C. of the washings. The funnel con- taining the yellow precipitate is then placed over the vessel in which the precipitation took place, and the filter washed with the smallest possible quantity of a warm 10 per cent. ammonia solution until the precipitate completely dissolves.By careful working, this can be accomplished in three or four washings. The filter is then washed sufficiently (seven or eight times) with hot water. If the ammonia used in washing is insufficient to dissolve the yellow precipitate in the beaker, more must be added, and should the solution not be clear, it must be passed a ,second time through the same filter. The solution (which will be still warm) is as nearly as possible neutralized with hydrochloric acid (until the precipitate produced on the addition of a drop redissolves with difficulty), cooled, 25 C.C.of a 5 per cent. solution of ammonia added, and 20 C.C. magnesia mixture added drop by drop. After two hours' standing (or half an hour's shaking with the shaking machine), the precipitate is filtered off and washed with a 5 per cent. solution of ammonia until chlorine is no longer found in the filtrate. The precipitate is dried at 100" C., transferred to a platinum crucible, the filter-paper separately burnt, and the whole incinerated over the flame of a powerful burner. By the use of the Gooch (perforated) crucibles, the precipitate is both dried and ignited in the crucible. The crucible is finally heated for five minutes in a muffle or over the blow-pipe, taking care that if the blow-pipe is used, reducing gases do not find their way into the crucible.It is then cooled and weighed. The ignition must be repeated until the weight remains constant. 4. The Citrate Method.-Preparation of the Solution.-Five hundred and fifty grttmmes of pure citric acid are dissolved in 2,000 grammes of a, 24 per cent.130 THE ANALYST. ammonia solution (0.91' specific gravity), made up to 5 litres with water and filtered. Dctcwnination.-For substances containing up to 20 per cent. phosphoric acid, 50 C.C. of the prepared solution, corresponding to 1 gramme of substance, are to be taken; for substances containing more than 20 per cent. phosphoric acid, 25 C.C. = 0.5 gramme of substance. Fifty C.C. citrate solution are added, and 25 C.C. magnesia mixture (as described under the niolybdate method). The whole is then either stirred in a beaker, or shaken in an Erlenmeyer flask, for half an hour, allowed to stand for one hour and filtered.The 25 C.C. magnesia mixture should be added drop by drop, and allowed to fall into the middle of the liquid, to counteract the tendency of the precipitate to attach itself to the sides of the vessel. The ammonium magnesium phosphate is collected on a filter, as directed for the molybdate method, and washed with a 5 per cent. ammonia solution until the washings are free from lime and chlorine. The precipitate is further treated--i.e., dried, ignited, and weighed- exactly as described for the molybdate method. 5. The Umnizmb Method.-This method, though superseded, is nevertheless useful for testing superphosphates if moderately Free from iron and alumina.By careful working, reliable results can be very quickly obtained with it, and on this account it is reconimended for factory purposes. Fifty C.C. of the solution, corresponding to 1 gremme of substance, are placed in a beaker and 12.5 C.C. of an acid solution of ammonium acetate added. When the precipitate produced has subsided, the liquid is filtered into a 400 C.C. or 500 C.C. flask and the precipitate washed with hot water until the washings are neutral. Standard solution of uranium nitrate is then added to the filtrate and washings, and the whole raised to the boil. The addition of the uranium solution is now continued until a drop or two taken out gives the usual reaction with potassium ferrocyanide. The quantity of uranium solution used indicates the percentage of phosphoric acid. The filter containing the precipitate is then burnt in the usual way and weighed, half its weight being taken as phosphoric acid and added to the phosphoric acid found by titration.Preparation of the Bcagents. - Uyaizizmz, Sohtioiz. --Five hundred grammes chemically pure uranium oxide are dissolved in 13 to 14 litres of water to which 50 C.C. of concentrated nitric acid (1-4 specific gravity) have been added. The value of this solution is found by standardizing with a solution of monocalcium phosphate in which the phosphoric acid has been determined gravimetrically in 50 C.C. A superphosphate solution free from iron may also be used for this purpose. The solution of monocalcium phosphate can be prepared by digesting 5.5 grammes of dry tricalcium phosphate in dilute sulphuric acid, making up to a litre with water and filtering off the gypsum and insoluble matter.Acid Solution of ArrLnzonizLm Acetate.-One hundred grammes of chemically pure ammonium acetate are dissolved in 900 C.C. of water and made up to a litre with glacial acetic acid. SoZzLtion oj' Potassium Fe1.).oc7Jnil.itZe.-This solution, which must be freshly pre- pared every time before use, is made by dissolving 8 gramme chemically pureTHE ANALYST. 131 potassium ferrocyanide in about 40 C.C. of water. A good light is required for discerning the colour. 6. Determination of Cityate-soliiblc PhosplioTic Acid.-- Waguer's MetlmL-Five grammes of superphosphate or precipitated phosphate are rubbed into a paste with diluted citrate solution (prepared as directed) and washed into a half-litre flask.It is then made up to the mark with the diluted citrate solution, allowed to stand for about eighteen hours at the ordinary temperature (17" to 18" C ) , with frequent shaking, and filtered. (Thirty minutes in a shaking or stirring machine may, how- ever, be substituted for the eighteen hours' standing.) Fifty C.C. of the filtrate are then taken, and molybdenurn solution added in the proportion of 1 C.C. molybdenum solution for every inilligramme of phosphoric acid, and to this is added one-fourth of its volume of concentrated ammonium nitrate solution (to be presently described). It is then placed in a water-bath heated to 50" C. for about twenty minutes, taken out, cooled, and the precipitate filtered off and washed with dilute solution of ammonium nitrate.A hole is then made in the apex of the filter, and the pre- cipitate washed back into the beaker used for the precipitatioii by means of a 2$ per cent. solution of ammonia. The filter is well washed, and 20 C.C. magnesia mixture added to the ammoniacal solution drop by drop, with constant stirring. After standing for about an hour, the precipitate is filtered off, washed with a 2 per cent. ammonia solution, and dried and ignited in the usual way. Preparation of the necessary Solutions. - - (1) C'omeiztrated Citrate Solutiou.-One hundred and fifty grarnmes of citric acid are dissolved in water in a litre flask and the solution neutralized with ammonia. Ten gramines of citric acid are then added, and the whole made up to the mark with water.(2) Dilute Citrnte Solutioiz.-One volume of concentrated citrate solution diluted with four volumes of water. (3) Concentq.ated Ammoiiiiiwz Nitwte Soliitioiz. --Seven hundred and fifty grammes of ammonium nitrate are dissolved in water, and the solution made up to a litre. (4) MolySrlenu?iz SoZzition.-One hundred and fifty grammes of ammonium molybdate are dissolved in water, the solution made up to a litre, and mixed with a litre of nitric acid of 1.2 specific gravity. (5) Mupesin Niztzirc.-One hundred and ten gramines of pure crystallized magnesium chloride and 140 gramrnes of ammonium chloride are dissolved in 1300 C.C. of water, and 700 C.C. (8 per cent.) ammonia added. Belgian Met hod (Petermann's 1.*- zian tities to be Taken.-For superphosp hat es containing more than 20 per cent. phosphoric acid and for precipitated phosphates, 1 gramme ; for superphosphates with 10 to 20 per cent. phosphoric acid, 2 gremmes ; for superphosphates with less than 10 per cent. phosphoric acid, and for compound manures , 4 grammes. Exttractioiz.-The weighed portion is first rubbed up in a glass mortar. It is then very thoroughly rubbed up with a small quantity of water and filtered by decantation into a 250 C.C. flask. After being treated three times in this way with water, it is afterwards washed on to the filter, and there further washed until filtrate * Published by the Station Agronomicjue d ' h a t de Gembloux.THE ANALYST. and washings together amount to about 200 C.C.The filtrate and washings are then made up to the mark with water. The filter with the insoluble residue is placed in a 250 C.C. flask, and 100 C.C. of Petermann’s alkaline ammonium citrate solution added. The digestion of the residue in the citrate solution is carried out in two stages. First, it is allowed to stand for fifteen hours at the ordinary temperature, with occasional shaking, and afterwards digested for one hour at 40” C., the time being reckoned from the moment when the thermometer in the water-bath registers this temper at ur e . I’i.eci~itatioii.-The solution is cooled, filtered, and made up to 250 c.c., and 50 C.C. of this mixed with 50 C.C. of the above aqueous solution. (If it has become turbid, a few drops of nitric acid should be added.) The combined water-soluble and citrate-soluble phosphoric acid is then determined in the mixture, either by the molybdate or by the citrate method.Preparation of the Petembaiziz SolzLtion.-Five hundred grammes of citric acid are exactly neutralized with ammonia of 0.92 specific gravity ; about 700 C.C. are required. This is then cooled, adjusted to 1-09 specific gravity at 15” C., 50 C.C. of ammonia of 0.92 specific gravity added for each litre, and the whole filtered. 7. Deternzimtion of Phosphoric Acid awl Percentage of Fine Meal in Thonms Phosphate.-A. Dctemzinntion of Total Phospho?.ic Acid.-(a) Hydrochloric Acid JIet?zod.-Tht! sample is prepared for analysis by being rubbed up in a mortar and sifted through a No. 60 sieve (German gauge). Should any considerable quantity of iron remain, it must be weighed and taken into account. Ten grammes of the prepared sample and about 80 C.C. of concentrated hydrochloric acid are placed in a 50 C.C. flask and evaporated on a sand-bath until the solution is of about the consistence of syrup. A few drops of hydrochloric acid are then added, the solution cooled, made up to the mark with water, and filtered. Fifty C.C. of the filtrate are mixed with 100 C.C. of Naercker’s aiiimoniacal citrate solution (1,500 grammes citric acid and 5,000 C.C. 24 per cent. NH, made up to 15 litres) and 25 C.C. magnesia mixture, and placed under the stirring machine for half an hour. I t is then allowed to stand for two hours, filtered, and treated as described for the determination of the water-soluble phosphoric acid. ( b ) SzdpILzii*ic Acid Method.-Ten grammes of the phosphate are first thoroughly mixed with a few C.C. of dilute sulphuric acid (1 in 2), and then 50 C.C. of concentrated sulphuric acid are added. The mixture is then raised to the boil, and kept at a heat just below its boiling-point until evaporated to a thick fluid, which commences to buiiip violently. It is then made up with water, and further dealt with by the molybdate or the citrate method. (To be contiwed.)

ISSN:0003-2654    

DOI:10.1039/AN8962100128

出版商:RSC    

年代:1896

数据来源: RSC

摘要:

THE ANALYST. ABSTRACTS OF PAPERS PUBLISHED 133 IN OTHER JOURNALS. FOOD ANALYSIS. The Estimation of Alcohol and Extract in Wine by the Refractometer. E. Riegler. (Zeit. aiznl. Chenb., 1896, 27-31.)-1n this method the refractive power of the wine, of the residue freed from alcohol and made up to the original volume, and of distilled water are determined by means of a Pulfrich’s refractometer, and from these data the results are calculated. The refractive power of the wine =; N consists of three parts : 1. That corresponding to the distilled water=a. 2. 9 , ?, ,, extract -2 b. 3. I ’ 1 ) , , alcohol = c. From these : N - ( a + b ) = C = the part corresponding to the alcohol, and (a+b) -a=b= ,, 9 , ,, extract. From the examination of a large number of samples the author has obtained 1.One gramme of extract in 100 C.C. of wine raises the refractive power by 2. One gramme of alcohol in 100 C.C. of wine raises it by 0.00068. In making the determination 25 C.C. of the wine are evaporated to about 8 c.c., and the residue made up again to 25 C.C. The flasks containing this extract solution, the original wine, and the distilled water are placed in a vessel of water at the tem- perature of the room, so that all three liquids have the same temperature. The difference between the refractive power of the wine, N, and that of the extract solution (a + b), divided by 0.00068, gives the aiiiount of alcohol in gramnies in 100 C.C. of wine : the following factors which he uses in the calculation : 0.00145 as compared with that of water. N - (a+ b) = c. I_- ~ 0.00068 The difference between the refractive power of the extract solution (a+ b ) and that of the water, a , divided by 0-00145, gives the amount of extract in grarnmes in 100 C.C.of wine: a+b-a b 0.00145 = o.00145’ Examnple : Refractive power of wiiie = 1-34105 Refractive power of extract solution = 1.33550 Difference = 555 555 = 8.1617 gramines alcohol in 100 C.C. wine. 68 Refractive power of extract solution = 1.33550 287 I , ), distilled water = 1.33263 z7 - 1.9793 grammes extract in 100 C.C. wine. 145 -134 Extract Wine = N. Solution =(a + a). 1-34037 1.33558 1:34165 1.33517 1.33978 1.33459 1.34088 1.33500 THE ANALYST. The following table gives some of the results obtained in this way, compared Of IXs- tilled Water = (a). 1 '33254 1.33237 1.33238 1.33222 with those obtained by the ordinary methods : sp, Gr.at Extract in Alcohol in Grs. Qrs. 15" (7, 100 C.C. 100 C.C. 0-9963 2'0660 7*0206 0.9921 1'8800 9'4793 0-9932 1,6240 7.7400 0.9930 1 -8784 8'6443 Refraction raised as compred with Water by 1 Gr. Ex- tract in 100 C.C. Wine. 0'00147 0.00148 0.00137 0.00148 Refractirrn raised as compared with WPter by 1 GY. Alcohol in 100 C.C. Wine. 0 '00068 0 -00068 0-00067 0.00067 Extract Calcu- lated. Grs. per 100 C.C. 2.0965 1.9310 15242 1'9172 Alcohol Calcu- lated. Grs. per 100 C.C. 7.0441 9'5294 7'6324 8.6470 The author considers this method equally suitable for the examination of beer, but has not been able to test the results on a sufficient number of samples to enable him to speak positively. C. A. M. The Estimation of Lzevulose in Honey or Other Substances.H. W. Wiley. (JOZLT. 97ncr. Chem. SOC. , 1896,81-91. j-The principle of the process depends on the change in the specific rotatory power of lmndose at different temperatures. I n the author's apparatus the observation-tube was so constructed that it could be kept at the selected temperatures (zero and 88" C.) by means of a control medium, either water heated by a steam-jet or by ice. To avoid the deposition of moisture on the cover-glasses at the lower temperature, a tube of hard indiarubber was attached by means of a threaded screw to the ends of the observation-tube. This had a central axis of perforated brass of the same dimensions as the diameter of the observation- tube, outside of which were placed fragments of calcium chloride. The end of the tube was covered air-tight with an ordinary cover-glass.At the higher temperature an even temperature was maintained by means of a mechanical stirrer. Before making a polarimetric reading the observation-tube should be kept for a t least half an hour (sometimes longer), noticeably in the case of honey, at the required temperature. When solutions are to be read at a high temperature, the water sur- rounding the tube should have been recently boiled, so as to avoid the evolution of air-bubbles. A correction is made for the linear expansion and contraction of the tube at the temperature of observation. The general formula for the calculation of the percentage of lzevulose is : Where K = deviation in divisions of cane-sugar scale or in angular rotation pro- T and t = temperatures of observation.R = observed deviation in rotation. W =weight of lawulose obtained, L = percentage of lzevulose required. duced by 1 gramme of laevulose for 1" temperature. For most genuine honeys the value of R between 0" and 88" C. is approxiinately thirty divisions of the cane-sugar scale or 10" angular measure for 26-048 grammes inTHE ANALYST, 135 100 C.C. read in a 200 mm. tube, or for 13.024 grammes in 100 C.C. read in a 400 mm. tube. The angular variation produced by 1 gramme of levulose for 1" of temperature is 0.01256". For 88" C. this would be 1.10528". In the given case the angular deviation observed between 0" and 88" C. was 10.404". The weight of lzvulose present was 104.04 + 1.10529 = 9.413 grammes, and the percentage = 16.13. In cooling solutions of honey the maximum left-handed rotation is not reached as soon as the temperature reaches zero, but only after it has been kept at that temperature for two or three hours.They should therefore be left for that time before taking the reading. Ezample.-26.048 gramnies of honey taken. C. 4. M. The Composition of Rabbits' Fat. L. Drumel. (Bzd?. dc 1',4ss. beige des Its odour is The following constants Cliim., 1896, ix., 323.)-Rabbits' fat is white, or occasionally yellowish. characteristic, and its consistency less than that of lard. were obtained by the author : Density at 100" C. ... ... ... ... ... Melting-point ... ... ... ... ... ... Temperature of solidification ... ... ... ... Refractive index (Zeiss) at 40" C.. . . ... . . . Insoluble fatty acids ... ... ... ... ... Volatile fatty acid (Reichert-Meissl No.) for 5 gramiiiea Insoluble fatty acids. solidification temperature ... f inelting-point ... ... ... 1 refractive index at 40" ... 0.861. 44-46" C. 28-30' C. 49. 95.47 per cent. 2.64 $iNaOH. 48-50" C. 39-41". 36. C. A, M. The Reaction for Sesame Oil. J. Wauters. (Bull. de 1'Ass. belye dcs c1ii?n., 1896, ix., 257-280.)-Baudouin's test-the red colour produced by the action of hydrochloric acid containing sugar in solution-though giving good results when the sesame oil is present in sufficient quantity, is not very reliable when small amounts are in question. I n 1893, Villavecchia and Fabris (ANALYST, xix. 47) studied the re- action, and found that the red colour was only produced when laevulose, or substances producing lzvulose when acidified, were used.With other sugars, such as glucose, maltose, and galactose, the test failed. They came to the conclusion that the principal factor in the reaction was furfurol, which is produced by the action of acid on certain kinds of sugar, notably laevulose and saccharose, and in Baudouin's test they employed a solution or' 2 grainmes of furfurol in 100 C.C. of alcohol instead of the sugar. The author has examined this modification, and confirms its accuracy and delicacy. He proceeds in the following manner : 10 C.C. of hydrochloric acid are mixed with 0.1 C.C. of the alcoholic solution of furfurol in a test-tube, 10 C.C. of the oil under examination added, and the whole allowed to stand.If sesame oil be present, the red colour is produced at the juncture of the two liquids. With 1 per cent. of sesame oil, the colour only appears after one or two minutes, but with 5 per cent. it is almost inst ant ctneous.136 THE ANALYST. With olive-oil, when fresh, no coloration is obtained, but with old and rancid samples there is a yellowish colour, which might possibly mask the addition of 1 per cent. of sesame oil, though 5 per cent. would be easily detected. I n examining butter, 10 C.C. are melted, filtered, and mixed with 10 C.C. of hydro- chloric acid and 0.1 C.C. of furfurol solution, the most suitable temperature being 40-45" C. Fresh butters give no coloration, and the addition of 0.25 per cent. of sesame oil is readily detected. With rancid butters a brownish-yellow colour is obtained, which might mask the addition of a very small amount of the oil. This reaction may also be employed conversely to detect furfurol in distilla- tion products, the alcohol to be examined being shaken with 10 C.C. of hydrochloric acid and 10 cc. of sesame oil. The author has obtained in this way a reaction with alcohol containing as little as 1 part of furfurol in 50,000. C. A. M.

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年代:1896

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136 THE ANALYST. ORGANIC ANALYSIS. On the Inversion of Sugar by Salts. J. H. Long. (Jour. Amer. Chem. Soc., 1896, xviii. 120-130.)-1t is well known that the specific rotation of cane-sugar solu- tions is decreased by the presence of many neutral salts, and K. Farnsteiner (Ber., xxiii. 3570) has noted the connection between the molecular weights of the salts dissolved with the sugar and the amount of depression produced. The author's experiments prove that temperature has a considerable influence, an inversion by means of ferrous iodide, which at the ordinary temperature requires months, being completed in less than two hours at 100" C. The rapidity of inversion is further increased by exposure to light. I n the experiments here summarized the solutions were heated in a, small flask with a perforated rubber stopper, having a capillary glass tube in the perforation.Ferrous Chloride.-Fifty grammes of cane sugar and 4.1 grarnmes of ferrous chloride in 100 C.C. Rotation in 100 mm. tube, 32-75". Rotation in same tube after one hour at 100" C., -6.42." Ferrous Bromide.-Fifty grammes saccharose ; 10 grarnmes of bromide in 100 C.C. Rotation=32-25". Ferrous SuZphnte.---Fifty grammes sugar, and 10 grammes of salt in 100 C.C. Rotation = 33". After heating for an hour protected from the air = 18.20". Ferrous Ammonium Su1phnte.-Fifty grammes sugar ; 10 of the salt in 100 C.C. Rotation = 33.08". The solution, after standing in a stoppered bottle for four months exposed to light, decreased in rotatory power to 7-53". Manggnnous Clzloride (4H,O).-Fifty grammes of sugar and of the salt.Rotation = 32.88". Mangmzous Szdphate ( + 4H,O).-Fifty grammes sugar + 10 grammes of crystal- lized sulphate. Rotation = 33.16". After one hour at 100" C., there was some decom- position, Rota- tion - 32.98. After one hour at 100" = - 10.26" at 20" C. After five hours at 71" C. = 27-20". After four months in the light = 1-66". Rotation, about +7" in 100 min. tube. Ziizc S.zdphnte.-Fifty gramines sugar, 10 grammes of the salt in 100 C.C. After forty-five minutes at 100" C = 18.42".THE ANALYST. 137 Potassium Aluminium SuZphate.-Sugar, 50 grammes ; alum, 5 grammes in 100 C.C. Lead Nitrate.-Sugar, 50 grammes; lead nitrate, 10 grammes in 100 C.C. Rota- tion = 33.13". Lead Chloride.-Sugar, 50 grammes; lead chloride, 2 grammes in 100 C.C.Rotation = 23.5". Cadmium Chloride.-Sugar, 50 grammes ; cadmium chloride, 8 grammes in 100 C.C. Rotation = 32-91". Mercuric ChZorzde.-Sugar, 50 grammes ; mercuric chloride, 5 grammes. Rota- tion=33.22". On heating at looo C., for some time there was a precipitate of mercurous chloride. Rotation of clear supernatant liquid = - 10.80. A second portion, heated for a shorter time till turbidity just commenced= - 4.82". The above salts, though neutral, have a weak base as compared with the acid, and the author's further experiments seem to point to strong sugar-solutions being inverted by such salts, on account of the partial hydrolysis of the latter by the solvent. By diluting the solutions, the results were much more uniform, approach- ing those obtained with weak acids alone.Rotation = 33". After one hour at 100" C. = - 9.99". After one hour at 100" C. = - 9.65". After heating = - 7-53", After heating to 100" C. = - 9-50". C. A. M. On the Determination of Nitrites in Potable Water. A. H. Gill and H. A. Richardson. (Jour. Awzer. Chem. Xoc., 1896, 21-23.)-1n the examination of a large number of samples by means of Trommsdorffs iodo-zinc starch method and Griess' a-naphthylamine test discrepancies were often observed, especially in the case of peaty water. Upon decolorizing the waters the results agreed, proving that peaty matter interfered with the formation of starch iodide, and that unless nitrites were present in considerable quantity they could not be detected by Trommsdorf's test. The decolorization was effected by shaking 250 C.C.of the water in the cold with '' milk of alumina," allowing to settle, and filtering through a filter which had been washed free from nitrites. The " milk of alumina ' I was prepared by precipi- tating a boiling solution of 125 grammss of potash alum per litre with ammonia, allowing the precipitate to settle, and washing by decantation. C. A. M. Examination of Oil of Bergamot. A. Borntrager. (Zed. anal. Chem., 1896, xxxv. 35-38.)-Bergamot oil owes its characteristic odour to the presence of linalol acetate, Cl,H170.C,H,0, the amount of which appears to be fairly constant. Prom the examination of a large number of Specimens, Schimmel and Co. gave this amount at 34 to 43 per cent., while the author found from 37.6 to 39.9 per cent.The deter- mination of this constituent is, therefore, a valuable means of detecting adulteration with oil of turpentine. From 1 to 2 grammes of the ethereal oil ere boiled with 10 t o 20 C.C. of semi-normal potash under a reflux condenser for one to two hours, and titrated back with semi-normal sulphuric acid, phenolphthalein being used as indi- cator. The amount of free acid in the bergamot oil is, as a rule, so trifling that it may be neglected. On evaporating bergamot oil on the water-bath, the residue should not be more than 6 per cent. of the weight taken. I n five specimens known to be genuine, the138 THE ANALYST. author found from 4.2 to 5.7 per cent. From 1 to 2 per cent. of saponifiable matter is contained in this residue, and this should be deducted from the amount of linalol acetate previously determined.A large amount of saponifiable matter in the residue would indicate adulteration with fatty oil. The addition of colophony would be shown by the residue being too high, and by the amount of free acids (nbietic, etc.) being more than normal. C. A. M. The Qualitative Examination of Acetanilide. C. Platt. (Jour. Amer. Chzem. Physical Characteristics.-Melts at 113" to 114" C. At 15" C. is soluble in about G'oncentrated Nitric Acid.-Readily soluble ; solution colourless when cold, but The cold solution gradually changes to red The red solution, on warnling, On Soc., 1896, xviii. 142-146.) 190 parts of water and in 5 parts of alcohol. changes to yellow and red on warming. on standing, with formation of red acicular crystals.gives off the odour of nitro-benzene, long standing the solution changes to pink or brown. Concentrated Szdphuric Acid.-Colourless solution, unaffected by boiling. Sulphurzc Acid and Po tns sium Bic hromate.--D ark-green solution. Hydrochloric Acid. -Readily soluble when warmed. Hydrochloric Acid and Potassium Permanganate. - Olive-green colour. Hydrochloric Acid and Chromic Acid,-On adding a weak solution of chromic acid to the hydrochloric acid solution, a green coloration is obtained. Potassium hydrate gives a blue precipitate in this solution. Hydrochloric Acid and Bromine.-Bromine water added to hydrochloric acid solution gives a heavy yellow-to-white precipitate of the mono-brom derivative of aniline. Hydrochloric Acid and Chlorine.-Dark-blue coloration, which afterwards fades.Potassium Hydrate.-Odour of aniline on heating. Sodium Nitrite and Sulphuric Acid.-The powder mixed with sodium nitrite, and sprinkled on concentrated sulphuric acid, gives a red colour. Ferric Chloride.-Produces no change when added to a cold saturated aqueous solution. Zinc Chloride.-Heated to 270" with an equal weight of acetanilide produces first ortho-amido-acetophenone (a yellow oil with high boiling-point) in small amount, and then flavaniline (CGH,,N,), a yellow substance with green fluorescence, a derivative of quinolin. The test of boiling acetanilide with zinc chloride, aniline, and acetic acid is considered untrustworthy by the author, who asserts that the reagents alone will produce amido - acet 0-p henone (C,H,N H,C,H,O). Plugge's Reagent.-Boil the acetanilide with water, filter, boil with potassium nitrite and dilute nitric acid. Mix with Plugge's reagent (a solution of mercurous nitrite with a little nitrous acid), and again boil. The foregoing tests readily distinguish acetanilide from antipyrin and phenacetin (cf. ANALYST, xxi. 69). A deep-red colour is produced. C. A. M.

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DOI:10.1039/AN8962100136

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年代:1896

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THE ANALYST. 139 INORGANIC ANALYSIS. Yellow Tint of Zinc-white. F. Fucks and F. Schiff. (Oest. 2. Berg. u. Hiitten-w., 1896,29 ; through Chem. Zeit. Rep., 1896, 42.)-The authors find that the yellow tint occasionally met with in zinc-white, and which has been hitherto attributed to the presence of ferric oxide, is due to minute traces of cadmium sulphide. Artificial mixtures prepared with cadmium and ferric oxide showed that the alteration in colour produced by these bodies was scarcely perceptible. W. J. S. Estimation of Manganese in Pig Iron. F. Ulzer and J. Brull. (Mittheil. techfa. Gew.-Mus,, Vienna, 1895, v., 312 ; through Chena. Zeit. Rep., 1896, 36.)-The solution, freed from iron by means of zinc oxide (Volhard's process, Fresenius, ii., 443), and containing about 0.1 gramme of manganese, is treated with 20 C.C.of 5 per cent. hydrogen peroxide, caustic soda added as long as a precipitate falls, boiled, cooled, and oxalic acid of known strength introduced. The precipitate is dissolved with pure dilute nitric acid, the solution heated to the boil, and the excess of oxalic acid titrated. The composition of the manganese precipitate may be taken as 5Mn0,Mn,07. To dissolve the original sample, 10 parts by volume of strong nitric acid, 2 parts of sulphuric acid, and 10 parts of water are employed, about 10 C.C. of hydrochloric acid being added during the evaporation. F. H. L. Analysis of Persulphates. F. Ulzer. (Mittheil. techn. Gew.-Mus., Viema, 1895, v., 310; through Chem. Zeit. Rep., 1896, 36.)-To determine the active oxygen, 0.3 gramme of the sample is heated with 1 to 1-5 granime of iron ammonium sulphate for half an hour in a current of carbon dioxide, and the unoxidized iron estimated with permanganate.In one par- ticular specimen of the ammonium salt, 3-20 per cent. of oxygen was found, equivalent to 45.61 per cent. of ammonium persulphate. For the total sulphuric acid, a fairly strong solution was heated with hydrochloric acid for some time, then precipitated with barium chloride, the yield being 70.01 per cent. The ammonia was 14.01 per cent., and the fixed residue 0-61 per cent. On titrating the aqueous solution with the aid of methyl orange, 18-93 per cent. of sulphuric acid was found. From these figures the composition of the substance works out as follows : The results agree within 0.2 per cent.Per Cent. Ammonium persulphate ... ... ... ... 45.61 bisulphate ... ... ... ... 48.77 1 , Fixed residue ... ... ... ... ... 0.61 Moisture ... ... ... ... ... 5.01 F. H. L. _ . - _ _ _ _ Silica a Cause of Scale in Boilers. A. Roichard. (Chem. Zeit., 1896, p. 65.) -The following instance shows that it is unsafe to judge of the fitness of a water for feeding boilers merely from the amount of calcium and magnesium salts which it contains. A water yielding a residue on incineration of 8.60 per 100,000, and con-140 THE ANALYST. taining lime 2.08, magnesia 0.22, silica 2.6, alkalies (weighed as chlorides) 2-35 parts, gave serious trouble in the formation of incrustation. The scale was found to consist chiefly of silica and lime. Weathered granite in the formation from whence the water was obtained was the cause of the large amount of silica and a1 kalies.W. J. S. Determination of Gold in Pottery Enamel. M. Schirmer. (Ann. da Chim. Analyt., i., 47.)-Owing to the presence of compounds, such as resinate of silver added to dilute or cheapen the enamel, an addition which may amount when fine gold is used-to 8 per cent. of metallic silver without exerting too great an influence on the colour, and especially to the mineral flux-most frequently a fusible salt of bismuth -which is always added to the enamel for the purpose of fixing the gold on the glass or porcelain surface, a simple incineration will not be sufficient to determine the gold. The following lriethod is recommended as giving satisfactory results : Ten grammes of the " liquid gold" to be tested is weighed rapidly in a large porcelain crucible, and evaporated on the sand-bath at a low temperature. The residue is then incinerated at the lowest possible temperature, since if the glaze on the crucible be softened some of the gold may be absorbed. The residue is taken up with cold aqua regia, and the solution, after dilution with water, is decanted on to a filter, and the residue treated once or twice with warm acid of the same strength. Finally, all the filtrates and washings are united, and the gold thrown down by ferrous sulphate in the usual manner. Should the inside of the crucible exhibit a violet or rosy coloration, indicating the absorption of gold by the glaze, it must be finely powdered and treated with cold aqua regia, the solution and washings being joined to the others; but this com- plication will not arise if the incineration has been properly performed. c. s.

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DOI:10.1039/AN8962100139

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年代:1896

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140 THE ANALYST. CORRESPONDENCE. TROPBOLINS IN MILK, ETC. T o the Editors of THE ANALYST. DEAR SIR,-In order to detect these dyes in milk it is of the greatest importance that the sample should be tested directly i t is received by the analyst, as the destruction of tropaeijlin, probably by the action of some ferment, commences very early in the decomposi- tion of the milk. I have observed that 10 C.C. of fresh milk (in winter) will consume in three days nearly 0-2 C.C. of solution of tropaeijlin (1 in l,OOO), this being enough of the dye to impart a very decided yellow or orange colour to the milk, and that the destruction afterwards proceeds much more rapidly. Boiling, after the action is well advanced, temporarily arrests for many days the destruction of the dye, but previous boiling of fresh milk only very slightly delays the commencement of the process. Yours faithfully, LESTER REED, F.I.C., F.C.S. CROYDON, Fehiaqj 25, 1896.

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DOI:10.1039/AN8962100140

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年代:1896

数据来源: RSC