摘要:

THE ANALYST. OCTOBER, 1888. PROCEEDINGS OF THE SOCIETY OF PUBLIC ANALYSTS. THE USE OF THE TERM “NORMAL” I N VOLUMETRIC ANALYSIB. BY ALFRED H. ALLEN, F.C.S., F.I.C. (Read at Neeting, July, 1888.) THERE is one point which has attracted my attention a good deal from time to time, and which appears to me a very proper subject for the Society of Public Analysts to con- sider, and even to express a formal opinion on. I refer to the definition of normal solutions. Unfortunately, the term ‘‘ normal,” as applied to volumetric solutions, is used in two distinctly different senses. By Mohr, whom we may regard as the father of volumetric analysis, and Sutton, whose book is best known to English chemists, the term is employed to signify a standard solution containing one equivalent of the active constituent in 1000 measures of water.The exact definition of a normal solution used by Sutton is that one litre at 16OC shall contain the hydrogen equivalent of the active reagent weighed in grams. (H=l). In Vol. I. of my Commercial Organic Aru;cZy&, I have practically adopted the same definition, describing a normal solution as ‘( one containing in 1000 C.C. such an amount of the active constituent as will combine with, replace, or oxidise one gramme of hydrogen.” Tollens similarly defines normal solutions as ‘I those containing in one litre that quantity in grammes of the active sub- stance which, in there action under consideration, is equivalent to one molecule, or 36.5 p m m e s of hydrochloric acid.” In the above definitions all normal solutions are of exactly corresponding strength, and those of a similar nature may be substituted one for another, volume for volume.Thus, according to this definition, which may be called the “equivalent system,” the following are the strengths of typical normal solutions : -182 THE ANALYST. Grms. per litre. Normal caustic soda contains Na =33 9 , 9 9 99 9 , NaHO =40 ,, sodium carbonate ,, Na = 23 =a2co, =53 9 , ?, 2 9 , 9 , ,, hydrochloric acid ,, HC1 =36*5 H2SO4 =49 9 , 2 ,, sulphuric acid 9 , H2C204, H2°=63 2 ,, oxalic acid Similarly, the following solutions are decinorma1:- Grms. per litre. =17*0 AgNO contains - 10 Decinormal silver nitrate ,, mercuric chloride ,, potassium permanganate ,, KMn04 50 = 3.162 ,, iodine ?, 9 , I =12.7 NazS203 + 5 H"o,24.8 99 10 ,, sodium thiosulphate ,, arsenious acid Ae203 = 4.95 4 By the other school, a normal solution is understood to mean a liquid containing the molecular weight in grammes in 1,000 C.C.By Fleischer, one of the advocates of this system, the old atomic weights are used, so that in most cases the strengths of his solution are the same rn those made on the equivalent system, but in the translation of Fleischer's book, by Mr. M. M. Pattison Muir, the modern atomic weights are used, with the consequence of very serious obscurity. Thus while normal caustic potash would contain 39.1 grammes of K per litre, we are told that " a normal solution of potassium carbonate is prepared by dissolving 138.2 grammes of potassium carbonate in 1,000 C.C. of distilled water. Hence such a solution contains 78.2 of K, and is twice as strong as the caustic alkali, or as the normal potassium carbonate of the original German.I n the original German, Fleischer calls a solution of 32 grammes of potassium permanganate in 1 litre 2T normal. It is true that this solution is absurdly strong, and iscapable of doing ten times the work attributed to it by the author. Mr. Muir has correoted this in an erratum, but in the text of his translation he actually doubles the strength of the above solution, recommending one containing 64 grammes per litre. That the nomenclature of a standard solution should vary aecording a% the writer employs the old or doubled atomic weights must be held to be highly inconvenient, to say the least of it, though Sutton (compare first with later editions), by employing the '6 equivalent system," has wholly avoided any such source of confusion, According to the The confusion is still greater when permanganate comes to be used,THE ANALYST.183 principle adopted by the “ molecular weight.” advocates, the employment of the same atomic weights will not always save us from confusion, for a standard solution of per- manganate will be differently called according as its employer considers the salt in solution to be KMnO,, or disregards its isomorphism with KCIO,, and prefers to write it KzMn,O,. Professor Dittmar, in his recently published work on “ Chemical Analysis,’’ wholly avoids the term normal, as he does also in his article on the subject in the new edition of I‘ Watts’ Dictionary of Chemical.” ‘Ur.Attfield also avoids the use of the term ‘‘ normal ” both in his Chemistry, and in the British Pharmacop&a, prefering to adopt round-about and not always very intelli- gible phrases in its place, In a paper by ‘C. Winkler (Berichte, xviii., 2,527), a short abstract of which appears in the Journal of the Chemical Society, vol. I., page 96, the author contends that the volumetric system should be derived from the molecular weights, and not from the equivalent weights as is the case at present. Tollens deprecates the pro- posed change (Jour. Chem. Xoc., I. 1,070) on the ground that it would cause confusion, and suggests the definition of a normal solution already quoted. Mr. John Pattinson evidently prefers the “ equivalent ” application of the term normal (Jour.Xoc. Chem. Ind., vi., 351.) The most recent support of the ‘‘ molecule ” content of normal solutions is that given by our esteemed ex-president, Dr. Muter, whose experience as a practical analyst and a teacher gives his opinion great weight. On page 105 OF the new edition (3rd) of his Manual of Analytical Chemistry he defines a normal solution as one (( having one molecular weight in gramrnes per litre.” The subsequent pages afford somo striking illustrations of the inconsistencies into which the supporters of this system are unavoid- ably driven. Thus every one knows that the molecule of iodine is Iz and has the weight 264, yet - solution of iodine is directed by Dr. Muter to be prepared with 12.7 grammes per litre, instead of 25.4 grammes.It would be interesting to know what strength the supporters of the ‘Lmolecule” definition would attribute to decinormal solution of arsenious acid. The solid substance, or white arsenic, according to many authorities has the molecular constitution Ase06, though it is more commonly looked on as As,O,. But the solution admittedly contains H,AsO,, or when neutralised Na AsO,. Query : Is a solution containing one, two, or four atoms of As in decigrammes per litre to be regarded as decinormal? By the 6‘ equivalent ” system of definition there is no difficulty, for a decinormal solution will be one which will react with an equal volume of decinormal iodine. According to the supporters of the ‘( molecule ” system, decinormal bichromate solu- tion will contain 29.5 gramrnes of K Cr,O, per litre. This will oxidise ?!!I- and hence be six times the strength of the solution similarly named on the equivalent system. But if used to precipitate lead or barium it will replace !!?! Here is an instance of confusion 10. in the case of the N 10 10 equivalent” nomenclature, I believe the only one. (Conclusion, of Society’s Proceedings.)

ISSN:0003-2654    

DOI:10.1039/AN888130181b

出版商:RSC    

年代:1888

数据来源: RSC

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184 THE ANALYST. QUANTITATlVE EBTIMATION OF PARAFFIN, CEROSIN, AND MINERAL OILS I N FATS AND WAX. BY F. 31. HORN.* THE processes devised by Geissler give inaccurate results. The proposal of Allen and Thomson to treat the dried soap with petroleum ether (volatile at SOW.) gives, according to Benedikt, useful results in the estimation of tho unsaponifiiable principles of pure animal and vegetable oils, but is not to be trusted if these contain mineral oils, because their soaps are partly soluble in petroleum ether. Instead of using petroleum ether, it has been tried to treat the soap in a Soxhlet's apparatus, with boiling chloroform, in order to extract the paraffin. The test analyses were very satisfactory, and gave results within *2 per cent, To insure rapid and complete saponification the following plan will be found advantageous :-About 6 grammes of the sample to ba tested is put in a porcelain disb, a piece of caustic soda weighing about 3 grammes is added, and after adding 80 C.C.of alcohol, the whole is heated on a waterbath, and well stirred with a glass rod. The saponification goes on veryquickly, and it does not take long befora the soap is quite dry. The excess of alkali is gradually made into carbonate by the carbonic acid of the atmosphere. When dry, the soap is put iiito a filter-paper cartridge. The basin may be rinsed with EL little chloroform, which is then poured into the mass after it has been put into the Soxhlet. The extraction by means of chloroform now goes on as usual ; and if the liquid should b3 turbid, it must be filtered.After evaporating the chloroform in a weighed dish, and drying residue at llO"C., the residue may be weighed. The quantity of paraffin in composite candles may be very accurately determined by this process. I n applying the process to wax, it must be remembered that beeswax contains about 50 per cent. of unsaponifiable matter (myricylic alcohol), which is soluble in chloroform. This must, of course, be separated from the paraffin. 6 grammes of the suspected wax are saponified as described, and extracted. The residue from the evapora- tion of the chloroform is boiled with acetic anhydride, when everything fuses. The myricy lic alcohol is, however, gradually converted into an acetate, and dissolves ; whilst the paraffin collects in drops on the surface of the fluid.The mixture must now be filtered through a thick filter (the funnel t o be surrounded by hot water), and the paraffin thoroughly washed with acetic anhydride. When sufficiently washed, the acetic acid is removed by washing with boiling water. No loss in paraffin is to he feared as long as the filter contains some water; but if allowed to run dry, paraffin may go through the paper. When all acid has been removed, the filter is put into a small beaker, dried a t 100°C., and the paraffin extracted by petroleum ether or chloroform, After evaporating off the solvent, the residue is dried and weighed. Instead of using acetic anhydride, glacial acetic acid may be used; but as the myricylic acetate is then far less soluble, it is mom difficult to wash out. Addition of sand or sodium carbonate is superfluous, The cartridge must be closed at the bottom, but not on the top.THE ANALYST. 185 The process succeeds equally well in presence of rosin, which is almost invariably present with the parafin. Tallow and 22 7 per cent. paraffin ... ... ... 22.6 per cent. paraffin Castor oil and 20.6 ,, vaseline oil ... ... 20.4 ,, vaseline oil Cotton oil and 14.23 ,, mineral oil ... ... 14.4 ,, mineral oil Beeswax and 17.42 ,, parafin ... ... ... 17.88 ,, paraffiu TEST API’ALYSES. Mixture consisting of- Found. Stearic acid and 9.5s ,, 9 9 ... ... ... 9.75 ,, 9 , White wax and 19.20 ,, Y, . . I ,.. , * . 19.1 ,, J Wax, rosia, and 14.0 ,, ,? .., ... ... 14.2 97 ?>

ISSN:0003-2654    

DOI:10.1039/AN8881300184

出版商:RSC    

年代:1888

数据来源: RSC

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THE ANALYST. 185 NEW METHOD FOR THE DETERMINATION OF CARBONIC ACID I N THE AIR. BY G. LUNGE AND A. ZECKENDORF.* IT is a well-known fact that a rapici estimation of the carbonic acid in the air, withmt complicated apparatus, is still a desideratum From a hygienic point OF view. A process devised by R. Angus Smith, slightly modified by one of uq, was published in German in 1877. The minimetric apparatus then described was based on the fact that the purer the air the more volume of it is required to cause a decided turbidity with lime or baryta water, The difficulty is, however, to notice the exact moment turbidity sets in, and therefore one of us searched in vain for an indicator to show the exact; point. Bloch- mann, Ba116, Schaffer, and Wolpert have devised apparatus, which are, however, either far too complicated €or the use of sanitary inspectors (without being, after all, very accurate) or very simple but very imperfect. Some of them, having been patented, are also rather expensive.The consequence is that officials who ought to use them, as a rule, do not trouble about the matter. As will be seen, one of us has succeeded in perfecting the popular minimetric apparatus, but we will first review some other processes. Blochmann makes use of a half-litre flask, into which small volumes of lime-water containing phenol-phthalein are successively poured, until the red colour no longer dis- appears. (One volume of the lime-water absorbs the normal quant.ity of the carbonio acid.) Ball6 also uses a half-litre flask connected with a burette, from which are delivered small portions of potash-lye, coloured with phenol-phthalein and containing some barium chloride.After every addition thc flask must be well shaken, until the liquid is decolorised. Both authors then simply report, Carbonic acid normal, or about so much in excess. Echaffer and Wolpert moisten a piece of blotting-paper with a solu- tion of sodium carbonate, coloured with phenol-phthalein, which will be gradually decolorised by the carbonic acid in the air, the carbonate passing into bi-carbonate. The more carbonic acid the air contains, the quicker the paper will lose its colour. The process, though simple, is not trustworthy, as it depends on too many circumstances, such as currents of air, and therefore may lead to great mistakes.Far better and even This was in 1876 and 1877. Since that time many chemists have proposed the use of phenol-phthalein,186 THE ANALYST. ~~~~ comparatively accurate results are obtained by the use of phenol-phthalein in the mini- metric apparatus. It is, however, plain that the apparatus in its old form is not well adapted for the purpose. With the old indiarubber ball of about 22 C.C. capacity, one must either work a very long time or use enormously diluted solutions, which may give rise to serious errors, as diluted solutions so soon decompose, and the change of colour then also becomes uncertain. Therefore we had to use a larger indiarubber pump. It has, further, been almost unavoidable to provide the pumps with valves, as they are used for mediciual purposes.Experiments carried out by Mr. Bertschinger proved those valves to be the best which were constructed on the system of tho heart. We now use an indiarubber pump provided with such valves, which may be still easily compressed with the hand, and still delivers a fairly constant volume of air, say from 70, 68, 72, 6S, 71,72, t o 71.5 c.c., therefore an average of 70.3 c.c., with an error of 1.7 c.c., which would only influence the fourth decimal of the percentage of carbonic acid. We have also made a mechanical pressing apparatus, by which the error may be reduced to -5 c.c., but this arrangement will only make the apparatus less suitable for those persons for whom it is really intended, without giving a corresponding advantage. The same may be said of the substitution of the indiarubber ball for a glass or metallic pump in the shape of a stomach-pump.The larger capacity of the new indiarubber pump, as compared with the old one, also rendered necessary the use of a larger flask. One having a capacity of 110 c.c., 10 C.C. for the reagent, and 100 C.C. for the air, proved satisfactory. We found it better not to draw the air through the apparatus, but to force it through. Flask A has I ring mark, showing 10 c.c., which volumo is, however, much better measured with a The illustration shows the apparatus (one quarter of its natural size).THE ANALYST. 187 pipette. Or the flask may be drawn out, which admits of a more accurate measuring of the fluid and a more thorough passage of the air, but its shape makes it, again, less practical.When the apparatus is required for use first press the indiarubber ball (B) with the right hand, and repeat this FL few times, that it may be filled with the air under examination. The flask is now opened, and 10 C.C. of the reagent are now introduced. After closing, the contents of B are now slowly pressed into A, which must be well shaken, more particularly towards the end. The red reagent, consting of 5z solution of sodium carbonate, containing *02 gramme of phenol-phthalein per litre, gradu- ally gets paler. If the air is very impure a couple of volumes b will completely decolourise it. In the case of moderately impure air, from 9-10 volumes will be required, for ordinaryair of the town about 25 volumes, whilst for pure country air, about 40 volumes will be required.In the latter case, a complete decolorising seldom succeeds, and one must cease transmitting more air, when the colour does not seem to fade any more. As, however, the testing of pure air is out OF the question, this nncertainty of the final reaction does not affect the process, and ttn excess of 3 volumes only affects the percentage about a005 per cent. The strength of the reagent as mentioned has provsd itself to be the best. If stronger, a very large volume of air must be passed through; if weak, it too soon decomposes. It is therefore better to use a 6 solution, made of 5.3 grammes dry sodium carbonate in one litre of water, with the addition of 1 gramme of phenol-phthalein dissolved in alcohol (to be added before the whole is made up to 1 litre) or this may be added in powder, and dissolved by gentle warming.Before use, 2 C.C. of this solution are diluted with water (free from CO,) up to 100 c.c., and 10 C.C. of this fluid used for each experiment. This sohition keeps a long time, but if it is some weeks or even days old it is safer to make it afresh. Lmg experience has taught us that the kind of glass is without influence, the solution keeping as well in Thuringen as in Bohemian glass bottles. As will be easily understood, the air previously contained in the flask A also takes part in the reaction; but a5 this quantity is constant, no correction was required in making up the table (see the end of this article). It must not, however, be imagined that the amount of CO, of the air may be aalculated from theorising that the sodium carbonate passes completely into bicarbonate.Percentages thus calculated are far from what they really are, and the more inaccurate the poorer the air is in carbonic acid. This is only quite natural, then it is not possible to combine tho last trace of sodium carbonate with the CO, even after prolonged shaking; in fact, solution of sodium hydro-carbonate when shaken with air free from CO, actually parts with traces of this gas. The relation between the number of fillings and the amount of carbonic acid had, therefore, to be ascertained by direct experiment. A small room, used for no other purposes, and to which there was no admission for strangers, was filled with air mixed with a definite amount of carbonic acid. The air was thoroughly mixed by means of moving a large cardboard, and the CO, estimated twice with the minimetric apparatus.Six litres of the air were then collected for the pur- pose of later on estimating the CO, by Pettenkofer’s process, and then two more mini- metric estimations were performed. OF the following experiments, the first one was not quite satisfactory, through want oE practice and insufficient mixing of the air. N N188 THE ANALYST. Carbonic Acid by No. NO. NO. N O . No. No. NO. N O . N O . No. No. NO. N O . Number of Volumes of Air with the Minimetric Apparatus. 1 48 49 48 2 25 25 24 3 26 25 26 26 4 20 21 20 20 5 17 17 18 17 6 13 13 12 7 10 9 10 10 9 8 10 11 10 10 11 9 8 8 9 9 1 0 8 8 8 11 8 8 12 6 6 6 13 2 2 2 Pettenkofer's Process Average.(parts in 10,000). 48 3.01" 25 5.32-j- 36 5.96-f. 20 6.62 17 6.91 13 8-06 1 0 8-90 10 9.15 8.5 11-28 8 11-70 8 11.70 6 15-55 2 30.0 -------I From the graphic illustration it will be noticed the results may be expressed by a well- defined curve, the only deviation being No. 3 ; but as we have already explained, with a pure air like this the end reaction is not so easily noticed and the error but very small. One may, therefore, construct by graphic interpolation a table which gives for a given number of fillings the quantity of carbonic acid. This table is, of course, only suited for an apparatus of the samesize as we have used, which may be obtained for 7s. 6d. from J. G. Cramer, in Zurich. For different- sized apparatus, other tables must be constructed. It mixst be further mentioned that our experi- ments were done a t a temperature of about 18" C, which, however, mill be the average tem- perature of most localities to be tested, so no correction will be required.The barometric pressure was about 730 mm. Great differences in pressure in other localities may necessitate a may be safely disregarded. 0.10 0 5 Table showing the Percentage of Carbonic Acid (Pettenkofer) Corresponding with every Ei'ZZing of the Ball of the lllinimetric Apparatus. No. of Fillings: CO, per cent. 2 . . .. ,. .30 3 .. * . .. *a5 4 . . .. * . -21 5 .. * . .. -18 6 . . .. .. *155 7 .. .. .. -135 8 r . .. . . -115 9 .. .. . . -100 10 * . .. . . -09 11 .. .. . . -087 12 . . .. . . *083 13 .. .. . . -08 14 .. .. . , -677 15 . . .. . . -074 I No. of Fillings, 16 .. 17 .. 18 .. 19 .. 20 .. 22 . , 24 .. 26 .. 28 . . 30 .. 35 . . 40 . , 48 . . CO, per cent,. * . .. *071 . . . , .069 a . . . -066 * . . . ,064 .. .. -062 . . .. -058 .. . . -054 .. . . 451 .. .. ,049 . . .. -048 .. . . *042 .. .. -038 .. .. -030 * Air from Zurichberg. t Air from the room without added CO,.THE ANALYST. lS9 I n conclusion, we must not omit to mention that wa have also tried the use of alcoholic solutions. As is well known, alcoholic alkaline solutions, colourad with phenol- phthalein, soon fade, which, according t o Draper, is caused by the abwrption of CO, from the air, which not only dissolves quicker in alcohol than in water, but also pre- cipitates alkaline carbonate. Dacdorisation, therefore, takes place long before the bicarbonate is formed. Our experiments have, however, shown that this reaction is useless to us, on account of its too great delicacy. Alcohol kept boiling for hours, and allowed to cool, with complete exclusion of CO,, still decolorised solution. It there- fore either retains CO, or its decolourising power must be caused by some other impurity. -

ISSN:0003-2654    

DOI:10.1039/AN8881300185

出版商:RSC    

年代:1888

数据来源: RSC

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THE ANALYST. lS9 ADULTERATION OF LARD WITH COCOA-NUT OIL. BY ALFRED H. ALLEN. 1 AM induced to make this communication, without waiting for a meeting of the Society of Public Analysts, on account of the very active interest now attaching to lard adultera- tion. I n the last edition OF my ‘I Commercial Organic Analysis ” (Vol. ii., page 142) the assertion is made that ‘‘ cocoa-nut oil has been employed for adulterating lard,” but I am unable to trace the authority on which I made the statement. Personally, I never found, nor, indeed, looked for, cocoa-nut oil in lard until quite recently, as I have regarded the peculiar odour or flavour of cocoa-nut oil as an inseparable barrier to its ucacknowledged use. A few weeks since I received a sample of lard for examination under the Sale of Food and Drugs Act, which, on analysis, gave the following results :- This difficulty is now surmounted..Water .. .. .. .. . . 0 86 per cent. Indicated plummet gravity a t 9 9 O c‘. .. *8666 Iodine absorption . . . . .. , . 37.4 per cent. Nitrate of silver test . . .. .. . . negative. These results were so extraordinary that I at once suspected the pressnce of cxoa- ON ORIGINAL FAT :- nut oil, and this suspicion was fully confirmed by the following additional data :- KHO required for saponification . . .. . . 21.15 per cent. = Saponification equivalent . . . . . . 265.2 Volume of E alkali required by the distillate from 2.5 grms. by the Reichert-Wollny process . , 3.3 C.C. Mean combining weight . . .. .. 6 . . . 253.04 Volume OF J alkali required by distillate from 5 grms.3 5 C.C. Plummet gravity a t 9 9 O . I . . .. .. *8400 Iodine absorption . . . . .. . . .. . . 48.5 per cent, ON SEPARATED FATTY ACIDS :- . . The volatile acids obtained by the Reichert-Wollny process contained a notable pro- portion of solid acids of sparing solubility in water, and had the characteristic odour of the distillate from cocoa-nut oil. I certified the sample to contain 33 per cent. of the adulterant. It is evident that the very characters which render it difficult to detect and deter- mine cocoa-nut oil in butter suffice to make its detection and determination in lard, even in presence of cotton-seed oil and tallow, a certain and fairly simple matter. This will be evident from an inspection of the following figures :--190 THE ANALYST. ORIGINAL FAT :- Lard.Cocoa-nut Oil. Plummet gravity a t 99" C. . . 0860 to 861 868 to 874 Saponification equivalent . . 286 to 292 209 to 228 Volume of 2 alkali required by Iodine absorption . . .. 55 to 61 9 distillate from 5 grms. . . 0.5 7.0 SEPARATED FATTY ACIDS :- Plummet gravity a t 99O C. . . -838 to 840 944 Iodine absorption . . .. 61 to 64 15.01 Mean combining weight . . 278 200 The most accurate determination of the cocoa-nut oil is obtainable from ths saponifi- cation equivalent, as this estimation is practically unaffected by the presence of cotton- Reed oil or tallow. Taking the average saponification equivalent of lard a t 289, and that of cocoa-nut oil a t 219, there is a difference of '70, and hence every 0.70 of fall in the equivalent below 289 indicates the probable presence of 1 per cent. of the adulterant. Comparatively small proportions of cocoa-nut oil in lard can be detected and safely cer- tified. In conclusion, I may add that some time since I received very pressing inquiries from America as to where cocoa-nut stearin could be obtained, but was compelled to reply that it mas not now in the market. was undoubtedly adulterated with cocoa-nut oil. Some months ago I met with a butter which 101, Leadenhall Street, E.C. September 19th, 1888.

ISSN:0003-2654    

DOI:10.1039/AN8881300189

出版商:RSC    

年代:1888

数据来源: RSC

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190 THE ANALYST. THE REMOVAL OF IODATE FROM THE IODIDE OF POTASSIUM BY MEANS OF ZINC AMALGAM. BY H. N. MORSE AND W. M. BURTON.* TEE frequent occurrence of the iodate of potassium in the commercial iodide, and the difficulty of removing it, are two of the most serious obstacles in the way of the freeuse of the iodometric method, either for quantitative ~ work, or for the detection of axidising agents. The fact that so many methods have been proposed for the preparation of iodide free from the iodate, and for the removal of the latter from the former, indicates that a simple and effective method for the preparation of the pure iodide of potassium is much needed, but not readily found. I n the course of our work upon the atomic weight of zinc it became necessary for us to prepare some iodide of potassium free from iodate, in order to test for the presence of the oxides of nitrogen, which Marignac? suppoaes to remain in the oxide of zinc pre- pared from the nitrate, even up to the dissociating temperature of the oxide.The method which we employed for the purpose consists in boiling the solution of the iodide with zinc amalgam. By this means the iodate is completely reduced with formation of zinc hydroxide, and the filtered solution is found to be free from both mercury and zinc. It is recommended to make the amalgam quite rich in zinc, and to have the filter paper through which the hot solution of iodide is to be filtered saturated with boiling water. * AmeTiann ChemicaZ Joumal. t Archives des Sciences I’hjs. et Nat (3) 10,195.THE ANALYST. 191 The efficacy of the method was tested upon solutions of pure iodate of potassium. In one case one gram. of tho iodate dissolved in 50 cubic centimetres of water was com- pletely reduced within forty-five minutes; in another, two grams. dissolved in the same amount of water were reduced within one hour and a quarter. The bromate and chlorate of potassium are also reduced by zinc amalgam, but much more slowly than the iodate. Of the two, the chlorate reduces less rapidly than the bromate. The zinc amalgam used in the reduction is best prepared by agitating zinc dust with mercury in the presence of tartaric acid, and washing with water.

ISSN:0003-2654    

DOI:10.1039/AN8881300190

出版商:RSC    

年代:1888

数据来源: RSC

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THE ANALYST. 191 A METHOD FOR THE ANALYSIS OF BUTTER, OLEOMARGARINE, ETC. BY H. M. MORSE AND W. M. BURTON." TEE method which we here describe has beon in use in this laboratory during the past year. Its advantages are : 1st. That it is volumetric throughout ; 2nd. That it obviates the necessity of weighing the specimen of fat ; 3rd. That it readily discriminates between genuine butter and any mixture of cocoanut oil and other fats or oils. That is, it suc- ceeds a t that point where the methods of Hehner and of Koettstorfer may fail. It depends upon the fact that the relative quantities of alkali required to neutralise the soluble and insoluble acids are for any one fat or oil quite constant, but for different fats or oils quite variable. The following statement contains the relative percentages of alkali required to neutraliso the soluble and insoluble acids of butter, cocanut oil, cotton-seed oil, gleo- margarine, lard, and beef tallow :- Per cent.KOH required for soluble acids. 1. Butter . . . 6 . 4 .. .: 86.57 13.17 2. Cocoanut oil (unwashed) .. . . 91.96 8.1 7 5. Cotton-seed oil . . . . . . . . 99.05 7.76 '7. Lard . . a . .. 6 . .. 95.96 3-82 8. Beef tallow , . .. .. .. 96.72 3.40 There is, between the amounts of alkali required to neutralise the solublo acids of butter and of unwashed cocoanut oil, a clear difference of 5 per cent. Evidently it would not be possible to make any mixture of the other substancos than butter in this list which would not show even a greater divergence from butter in respect to the soluble acids.The only way in which the proportion of soluble acids can be increased bgyond 8.17 per cent. is by the addition of butter itself. It was found by Moore that a mixture of butter 50 per cent., oleomargarine 27.5 per cent., and cocoanut oil 23.5 per cent., could not be distinguished from butter either by the method of Hehner or by that of Koettstorfer. Per cent. KOH required for Per cent. KOH required for insoluble acids. 3. Cocoanut oil (washed with hot water) . . 92.43 7.42 4. Cocoanut oil (washed with dilute Na,CO, 92 33 7.45 6, Oleomargarine . . . . .. . . 95.40 4 57 Such a mixture gave us :- Per cent. KOH required for iiisoluble acids. soluble acids. 90.1 7 9.70 I_- * American 6'hcnticnI Joirrmnl.- 198 THE ANALYST. ___-__ There is still a difference in respect to soluble acids of 3 47 per cent.between such a mixture and butter ; and it would not be practicable to so far increase the proportion of butter that there would not still be a perceptible difference in this respect between genuine butter and the mixture. The figures t’hus far given are mean quantities; we give in the following table the individual results from which they were calculated. The first column contains the number of milligrams. of potassium hydroxide required to eaponify one gram. of fat ; the second and third columns, the number of milligrams. required to neutralise the insoluble and soluble acids contained in one gram. of the fat ; while the fourth and fifth give the percentages corresponding to the quantities in two and three. 1. 2. 3.4. 5. 1. 2. 3. 4. 5. 1. 2. 3. 4. 5. 1. 2. 3. 4. 5. I. Mdgs. KOH for 1 gram. fat. 230.39 231.14 230.66 230.71 230.94 266.88 266.96 266.53 262.44 263.33 263 73 263.42 263.97 264.22 263.82 200.23 200.54 199 74 199.81 199.65 11. Mas. KOfI for iosoluble acids. 199.57 199.83 200.1 1 199.67 199.85 A. Butter. 111. Mgs. ROH for soluble acids. 30.21 30-94 30.07 30.54 30.29 IV. Per cent. KOH for insoluble acids. 86.62 86.45 S6.75 86.53 86.53 Mean, S6.57 v. Per cent. KOK for solnble acids, 13-1 1 13.38 13.04 13.23 13.11 13-17 B. Cocoanut Oil (unwashed). 245-50 21.91 9 1 *9s 5.20 244.87 22-01 9 1-72 8.24 245.68 21.53 92-15 8.07 Mean, 91-95 8.1 7 Cocoanut Oil (rashed with ho4 water). 243.17 19.11 92.65 7.28 242.84 19.91 92.2 1 7.56 Mesn, 92-43 7-42 -- Cocoanut Oil (sashed with dilute Na,CO,).243.27 19.91 92-24 7.54 243-39 19.31 92 *39 7.33 243.81 19.57 92.36 7-61 243.96 19.50 92.33 ‘7.38 243.61 20.03 92.33 7.59 Mean, 92.33 7-45 184.31 15.57 92.04 7.77 184.04 15.7 1 91-77 7 83 184.26 15-06 92 25 7.54 183.72 15.36 91.95 7.68 184.18 15.92 92.25 7.97 Mean, 92.05 7.76 -- -- C. Cotton-seed Oil.THE ANALYST. 193 1. 232 70 2. 202.61 3. 202.40 4. 202.62 5. 202.83 1. 199.77 2. 198.93 3. 199.54 4. 199.75 5. 199.40 1. 200.44 %. 199.70 3. 200.1 7 4. 199.60 5. 199.84 193.03 193.46 19331 193.65 193.27 191-78 191.11 191.29 191.63 191 34 193.43 193-20 193-81 193.13 193.42 D. Oleomccrgarine. 9-31 9 5 9 2 9.01 95-48 9 71 95 45 9.3 1 95.57 9 12 95.29 Mean, 95.40 7-31 96.00 7.9 1 96.06 7.71 95-86 7-87 95.93 7.1 7 95.97 Mean, 95.96 6.76 96.50 6,92 9G.74 6-47 96.82 6.9 1 96.76 7.01 96-78 Meaa, 96.72 E. Lard. -- F. Beef Tallow. -- 4.59 4.4 4 4.7 9 4.54 4.4 9 4.57 3.65 3.98 3-94 3 94 3.59 3-82 3.37 3.46 3.23 3.4 6 3.50 3-40 -- -- G. Jfikture : Oleomsrgarine 27.5 j Cocoanut Oil 22.5 ; But,ter 50 per cert. 1. 231. 208-77 22.65 90.37 9.81 2. 230.52 208.13 22.21 90.1 6 9.62 3. 231.15 208.1 1 22.76 90.04 9.84 4. 231.36 208.51 22.1 6 90.12 9.57 Mean, 90-17 9 70 Difference, 3.60 3.47 -- -- Percentages for pure butter, 86.67 13.17 _- -- (To be continued.)

ISSN:0003-2654    

DOI:10.1039/AN8881300191

出版商:RSC    

年代:1888

数据来源: RSC

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THE ANALYST. 193 ON SOURCES OF ERROR I N DETERMINATIONS OF NITROGEN BY SODA- LIME, AND MEANS FOR AVOIDING THEM. BY W. 0. ATWATER.* THE object of this paper, which concludes a series upon the same general subject, is to describe some further experiments in this laboratory, adduce results of observations elsewhere, and mention certain conclusions that seem warranted concerning sources of error in the determination of nitrogen in protein compounds, especially those of animal origin, by soda-lime, and the means by which they may be obviated. Leaving out of account the apparent gain of nitrogen which may come from impure soda-lime, or from obvious errors in manipulation, to be mentioned beyond, the prin- cipal sources of error involve loss cif nitrogen. Among the sources of loss are : * American C2emicaZ Joumal.194 THE ANALYST._ _ ~- 1. Incomplete ammonification of the nitrogen. 2. Dissociation or oxidation of the ammonia formed. 3. Failure of the ammonia to be completely caught and retained by the acid solution. Loss 6y Incomplete Ammonification of Nitrogen. Four ways suggest themselves by which nitrogen may fail to he changed into the 1. Incomplete decomposition of the nitrogenous substance, part of the nitrogen 2. Formation of compounds, e.g., cyanides, which remain in the tube. 3. Escape of nitrogen in the free st.ate. 4. Formation of volatile nitrogenous products other than ammonia, which either pass through the acid solution unabsorbed, or if absorbed, are not detected by the subsequent titration with alkali or other means used to find the amount of nitrogen in the solution.As no especial study of the first three of these sources of loss has been made here, I need only refer to them briefly. TO insure complete decomposition, fine pulverisation, thorough mixing with soda- lime, and heating, at sufficiently high temperature, until no charred residue remains, would seem t o be the requisites. As to the fineness of pulverisation needed there seem to be differences of opinion among chemists. Xitthausen" and Gruber?, for instance, lay great stress upon it. Gruber cites comparative determinations of nitrogen in flesh in which the incorrect results fell nearly 0.9 per cent. below the correct ones, and the only difference in the conduct of the analyses was that,. in the defective ones, the ' I Fleisch- pulver noch einzelne wahrnehmbare KGrnchen enthielt." Johnson and Jenkins, on the other hand, say that : " Contrary to what is commonly stated, fine pulverisation of the substance to be analysed is not necessary.If the substance will pass holes of om millimetre in diameter it is fine enough. A sample of dried blood which passed through a sieve with meshes one millimetre in diameter gave 7-55 per cent. of nitrogen. A por- tion of the same, ground extremely fine with sand, gave 7.64 per cent. Fish-scrap passed through the same sieve gave 8.98 per cent. of nitrogen ; when ground with sand, 8*95 per cent. A second sample of fish, sifted as above, gave 8.69 per cent. of nitrogen. By the absolute method it yielded 8-79 per cent.": The not inconsiderable experience of this laboratory confirms very decidedly the opinion last quoted.We have for a number of years used a sieve with circular apertures of one millimetre diameter. A large number of comparisons of results obtained by the soda-lime and absolute methods, and in a considerable number of cases with that of Kjeldahl, have given results so concordant as to persuade us that particlea which have passed through this sieve are fine enough. In absence of definite statements as to the actual fineness which is regarded as desirable by those who insist upon very fine pulverisation, I am inclined to suspect that. the standard adopted by Johnson and Jenkins, and in this laboratory, would perhaps be form of ammonia and may hence be lost in soda-lime determinations, namely, by : remaining in the partially decomposed (charred) residue.* Jour. prakt. Chem. 116, 1874, p. 17. -f Ztschr. f . Biol. 16, 380. 3 Report of Conn. Agl. Expt, Station, 1878 116THE ANALYST. 195 regarded as satisfactory in respect to fineness by them and by investigators generally. Certain it is that when, as in a number of instances, we have tried to use a sieve of one half millimetre aperture, we have found the process of grinding painfully laborious and time-consuming, even with the use of a mill especially devised for the purpose and exceeding in convenience all other forms which I have seen. As to formation of cganogen or other compounds which would be retained by combining with the bases of the soda-lime, I have been unable to find any experimental facts which would lead to the supposition that there is any considerable danger of loss in this way in the combustion of ordinary animal and vegetable substances, provided the soda-lime contains enough water, and the quantities of soda-lime and substance, tem- perature, and other conditions are appropriate.Regarding the escape of free nitrogen by decomposition of such nitrogenous compounds as those in question (leaving out of account the dissociation or oxidation of ammonia formed from them), I am likewise unable to find any facts which imply special danger of loss in this way, although it might, perhaps, be feared from such observations as that of Liebermann that albumin on being heated with caustic baryta to 150° yields free nitrogen." The main assurance that it does not escape to any great extent when the operation is rightly conducted, is found in the agreement of the results obtained with those obtained by other methods.The presence of nitrates, as impurities in soda-lime or otherwise, may cause loss of nitrogen, perhaps 11s free nitrogen, but this is of course simply a contingency to be feared from careless work. Loss of Nitrogen 6y Poormation of Volatile Products other than Ammonia. As long ago as 1860 Mulder called attention to the danger of loss by formation of volatile products which, escaping ammonification within the tube, were either not caught by the acid or, if retained, escaped determination by either titration with alkali or precipitation by platinic chloride.? About the same time Strecker observed that guanidine salts failed to yield all their nitrogen as ammonia with soda-lime.$ Ritthausen and Kreussler were unable to get more than 7.9 per cent.of nitrogen from leucine by soda-lime alone, even when the greatest care was taken to pulverise and mix it with the soda-lime, and 120 times as much soda-lime as substance was used. Adding sugar, however, they got as high as 10.43 per cent., very nearly the theoretical amount, and Ritthausen suggests that the trouble with leucine, as with other compounds, may be that volatile cleavage products are formed and pass over the soda-lime without their nitrogen being changed to ammonia.$ Marcker insists that aniline-like products may be given off instead of ammonia, and finds proof of this in observations that some substances, as for instance gluten and leucine, gave nearly or quite their full amount of nitrogen with platinic chloride, while there was decided loss by titration with alkali.With blood albumen and horse-flesh, however, there was a loss by titration which the platinic chloride did not amend, and - * Jbt. Ag. Chem. 21, 766. See also Wanklyn and Gamgee, J. Chem. SOC. 21, 1868, 25. t Chem. Centrbl. 1861, 44, $ Ann. Chem. (Liebeg) 118, 1861, 161. fj J. prakt. Chem. 111, 1871,310.196 THE ANALYST. which can be explained by assuming that products were formed which are not precipi- tated by the platinic chloride, which does precipitate aniline and kindred compounds.* Among the materials in which Nowack and Seegen failed to obtain the normal quantity of nitrogen (see beyond) by soda-lime was barium kynurenate.Gruber very aptly remarks that as kynurenic acid has been shown to be a derivative of quinoline, the failure may have been due to distillation of the latter.? %. Salkowski suggests that in determinations of albuminoids by soda-lime, bases of the pyridine series may be formed and escape ammonification. He also suggests that a substance with red colour which he obtained in burning at low lieat with a small quantity of soda-lime may perhaps be the chromogen of urobilin.: Kjeldahl in the discussion of his method for nitrogen determinations, referring to Mulder’s advice to avoid any large amount of vacant space inside the combustion tube, states a very interesting observation of his own. In making combustions of quinine- hydro-chloride with soda-lime, he found that when the soda-lime was loosely packed and shaken so as to leave a channel in the ordinary way, he obtained only about one half the nitrogen, while with the conditions in every respect the same except that the tube was well packed with soda-lime so as to leave a minimum of vacant space, he obtained practically the whole of the nitrogen as ammonia by titration. He attributes the loss in the first instance to the formation of volatile nitrogenous products which, not being brought into intimate contact with the soda-lime, escaped ammonification 9 (2’0 6e continued.) * Archiv Physiol. (Pfluger) 8, 1874, 207. $ Ztschr. anal. Chem. 16, 261 and 408. Ztscilr. f . Biol. 16, 1880, 377. $ Z!schr. anal. Chem. 22,1883,380. See also Arnold, Ber. d. chem. Ges. 18, 2886, 809.

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DOI:10.1039/AN8881300193

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年代:1888

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196 THE ANALYST. ON THE RELATIVE VALUE OF DIFFERENT PEPSIN TESTS. BY JAMES H. STEBBINS, Jzt.11 TEE gastric juice, secreted by the peptic glands of the stomach, contains two important principles-viz., hydrochloric acid and a ferment called pepsin. By the combined action of these two principles it performs its physiological function, which consists in digesting albuminoid matters; i.e., it dhintegrates, dissolves, and converts them into soluble, non-coagulable products, known as peptones. Wasmann first insolated pepsin in 1839, but it must be said that his process, as well as those which have since been proposed for the preparation of this article, do not furnish perfectly pure pepsin. The product obtained is always more or less mixed with extractive matter, mineral matter, and peptone, sometimes in considerable quantity, which our present knowledge of the art has not enabled us to completely remove.Perfectly pure pepsin is, therefore, not known, but we are nevertheless enabled to prepare products of very high digestive power. Many methods have been proposed for testing pepsin, but none of them are perfectly satisfactory. Thus, Bidder and Schmidt place a known weight of small cubes of coagulated white of egg in contact with a liquid containing a known weight of pepsin, dissolved inTHE ANALYST. 197 hydrochloric acid of 0.2 per cent. strength, and heat the mixture for about five hours at 45" C. The loss in weight of this albumen indicates the digestive power of the pepsin. This method of assay has the inconvenience of taking into account only the amount of albumen dissolved, without paying attention to the amount of albumen really con- verted into peptone.Griinhagen allows fibrin to swell in hydrochloric acid of 0 2 per cent. strength, and places the thick jelly thus obtained in a funnel, closed at one end with a little glass wool, and exposes the whole in a drying oven to a heat of 45" C. After all excess of water has drained off, a certain number of drops of a solution, containing the pepsin under examination, is allowed to trickle upon the jelly contained in the funnel. I n about two minutes the liquid will begin to drop from the funnel, and the rate of dropping in a given time is said t o be proportional to the strength or activity cif the pepsin. P. Griitzner determines the value of pepsins by allowing flocks of fibrin, stained with carmine, to digest under similar conditions, and then estimating colourimetrically, at the end of a certain time, the intensity of the colouration of the liquid separated by decantation from the non-dissolved fibrin, by comparing it with a certain number of standard solutions of carmine.It is very easy to stain fibrin evenly with carmine, and therefore the intensity of the colouration of the solution is proportional to the amount of fibrin dissolved by the pepsin. The methods I propose to discuss in this paper are three; viz , the U. S. P, test, the Manwaring test, and the Kremel test. According to the experiments of numerous investigators, the peptic digestion of albuminoids depends upon several conditions.1. The temperature. The pepsin of fish acts energetically at 20" C., but the pepsin of mammals requires a higher temperature, and it has been found that peptonisation is most active between 350 C.-50° C. Above this, digestion runs much slower, and ceases totally towarda t o -soo c. A t the end of this time the non-dissolved albumen is washed and weighed. The same applies also to the two following methods :- 2. The quantity of pepsin. There being no such thing as absolutely pure pepsin, i t has been impossible to determine with accuracy the amount of albumen which can be converted into peptone by a given quantity of the ferment. We know only that the amount is very large, provided that from time to time a little acid and water is added in order to maintain a certain degree of dilution. The quantity of albuminoid which can be digested in a given time increases rapidly with the quantity of pepsin employed till it reaches a maximum, and then decreases slowly.The quantity of peptone finally obtained increases with the proportion of pepsin. 3. The quantity of water. As the products of digestion accumulate the rate of peptonisation gradually decreases. The addition of a fresh quantity of acidulated water causes the peptic action to recommence, until it has reached a certain limit, beyond which the reaction ceases entirely. 4. The nature and quantity of the acid used.198 THE ANALYST. A large number of acids may take the place of hydrochloric acid in peptic digestions, but none of ’them are as efficient as the latter.A. Mayer found that with the use of hydrochloric acid complete peptonisation occurred in from 3 to 5 hours, with nitric acid in about 5 hours, with oxalic acid in 13 hours, and with mlphuric acid in 19 hours. According to Brucke, peptonisation is already very active in a medium containing only 0.8 pts. of hydrochloric acid per 1,000, and attains its maximum with a concentra- tion of 1 pt. of acid in 1,000 of water. A too large proportion of acid hinders peptonisation, 7 pts. of acid per 1,000 of water being sufficient to make the action very slow. Mayer thinks that the most favourable proportion of acid is 2 pts. per 1,000 water, or 0.2 per cent. 5. The time of action. 6. The variety and character OF the albumen. One of the most largely used tests in this country is the U.S, P. test, which reads as follows :- (( One pt. of saccharated pepsin, dissolved in 500 pts. of water, acidulated with 7.5 pts. of hydrochloric acid, should digest at least 50 pts. of hard-boiled egg albumen, in 5 or 6 hours, at 100-104° F. (3’7*5-40° C.) ” The above test seems simple, but in reality it is unreliable and misleading, as no two persons using the ~ a m e pepsin can obtain the same or even approximate results; it is, therefore, not surprising that we meet with such a diversity of conclusions. The weak points in tho above test are the following :- 1. The test is based upon the amount of albumen which can be dissolved in a given time (including peptone and intermediary products), but does not take into con- sideration the amount of peptono actually formed, and this I claim to be of the greatest importance.2. It directs that a given pepsin shall digest at least 50 pts. of coagulated albumen, Now, in order to determine how much albumen has actually been dissolved, i t is necessary to use an excess of albumen, and then weigh what remains undissolved. The test in question does not specify how much albumen shall be used, but leaves it entirely to the option of the experimenter. I consider this to be a weak point, as it makes quite a, difference whether only a small or large quantity of albumen is used. 3. It is difficult to see how accurate results are to be obtained by weighing the amount of undissolved albumen remaining after a digestion, because it is impossible to find two samples of coagulated albumen which contain exactly the same quantity of moisture; and besides this, the quantity of moisture is very liable to vary during the weighing, owing to the loss of moisture by evaporation. This is a very important matter, as digestion differs greatly according to whether the eggs are boiled for a short or a longer time. This, also, is very important, as it has been found that the greater the surface of the albumen exposed to the peptic ferment, the greater will be the amount of albumen digested. 6, This test applies only to saccharated pepsins, and no provision is made for other brands of pepsin. It will, therefore, be seen that the U. S. P. pepsin test is absolutely unreliable and misleading. 4. It is not stated how long the eggs shall be boiled I 5. No provision is made for the size of the pieces of coagulated albumen. (To be continued.)

ISSN:0003-2654    

DOI:10.1039/AN8881300196

出版商:RSC    

年代:1888

数据来源: RSC

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THE ANALYST. 199 MONTHLY RECORD OF ANALYTICAL RESEARCHES INTO FOOD. FLOUR IN SAUSAGES. H. TRILLICH. Zeitschr. f. ccngew Chemie, No. 17.-The idea that it is possible to introduce a large amount of water in sausages by means of flour is also shared by Dammer, in his Lexicon der Verfalschungen. Schmidt and Muhlheim, in their work on meat and meat preparations, say 1 part of flour is capable of holding 60 parts of water. So a sausage may look all right, but still contain, say, 67 per cent. of water. The author proved, last year, that a small quantity of added flour has no influence on the quantity of water the sausage is capable of holding. If the water is calculated from the amount of added flour the result is, of course, too low, and the true amount is got by adding the water combined with the meat.I f the flour is capable of holding 67 per cent. of water, then, as the average percentage of water in fresh meat is 64, the total percentage of water will be-- 67 + 'E4 = 84.3 per cent. 100 The author's analyses of Miinchener sausages sometimes showed 76.5 per cent. of moisture; but even if they also contained 6 per cent. of flour their appearance soon betrayed them. A sausage with 83-84 per cent. of water is, in fact, not a saleable article. If, however, the 27 per cent. of meat means dry substance, then it will be im- possible to pretend that all the water is in combination with the flour; then 27 per cent. dry meat represents 75 per cent. fresh meat with 64 per cent. of moisture, and therefore 48 per cent. may be taken as the natural amount of water in the used meat, The remaining 19 per cent.must have been introduced in the sausage by some device or other; but it is not necessary to use flour for this purpose. The water absorption (binding) power of meat is 25.3 per cent. Supposing it to contain less natural moisture- say only 50 per cent.-it would not, as may be supposed, have a larger absorption power, but, as experience has taught, rather a smaller one. Calculation of the water a6sorption power of sausage meat.-Taking the moisture of meat to be 60 per cent., then, if a represents the moisture of the sausage, and 8 the amount of added flour, the absorption power will be- Y=a - 1.5 (100-a-s) per cent. a For a different percentage of moisture in the meat, replace 1.5 by ~ The absorption power for the starch-free article will be- 100 - a' ( I 100-s I -2.5 1100-a-8 I ) 2 - - I-._ 2.5 1 100 -a - a 1 a 2.5, if required, to be replaced by To get trustworthy results, examine the sausage when quite fresh. L. DE K,

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DOI:10.1039/AN8881300199

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年代:1888

数据来源: RSC

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200 THE ANALYST. ~ CORRESPONDENCE. [The EditoT is not in any way responsible for opinions expyessed by his corpespondents.] POLLUTED DRINKING WATER AND THE CLOSURE OF WELLS. To the Editor of the ANALYST. SIR, -In my paper on this subject, read at the meeting of the Society of Public Analysts on June 20th, 1888, reference is made to the case of a wellat Enfield, the water of which was pronounced by one chemist as “ containing sewage, and totally unfit for drinking purposes,” while another, whose analytical results were essentially the same, reported it 4t a perfectly safe water to use for drinking and domestic purposes, being free from all traces of sewage contamination.” Owing to this conflict of evidence the magistrate referred the case to Dr. Bell, of Somerset House. I n my paper I say, “ singularly enough, two other chemists, whose analytical results agree with Mr Lloyd’s, gave favourable reports of the water.” Dr.Bell, in a letter to me, complains that this remark entirely misrepresents the terms of his report. While disclaiming, as I hope is hardly necessary, any intention to mis- represent Dr. Bell’s views, I may state that I made the remark without having seen the report, and on the strength of a paper read by Mr. Lloyd at a meeting of the Society of Medical Officers of Health, and the report of this in the British Medical Journal of May 26th. The dismissal of the case by the magistrates after receiving Dr. Bell’s report, con- firmed in my mind the impression made upon it. Dr. Bell has sent me the following extract from his report :- t i The organic impurity present, as indicated both by the albuminoid ammonia and the oxygen consumed, does not exceed by an appreciable extent the limit allowable in a potable water.“ From the large quantity of saline matters present in the water, including nitrates, chlorides, and salts of ammonia, it is evident that it passes through a stratum of earth largely charged with sewage or organic refuse substances, and carries down with it various products resulting from the oxidation of the organic matter. “ These products, although not absolutely dangerous to health, are very objectionable in water intended for domestic purposes, and when present to the extent in which they exist in the water under consideration, we should not recommend it for use for potable purposes. “ Although, therefore, we are unable to entirely agree with the opinion pronounced by either analyst, we should advise the discontinuance of the use of the water on account of its unsatisfactory and doubtful character.” It is clear from the last two paragraphs of the report that, though Dr.Bell does not condemn the water as dangerous, he does not give that favourable report of it which the information at my command led me to understand.-I remain, Yours faithfully, ALFRED HILL. Borough of Birmingham Health Department, The Council House, September 22nd, 1888. TEST FOR THE PURITY OF MILK.-The fashion of empirical tests has quite set in and the following paragraph has been going the round of the prew :-“ A very simple and ingenious method of testing whether milk has been adulterated with water has been an- nounced by a German scientist, who says it will detect the presence of the smallest quantity of the objectionable ‘ Simpson.’ The plan recommended is to place the milk in a deep vessel, and procuring a highly polished knitting needle, to insert it vertically in the doubtful fluid. The needle must then be steadily withdrawn, and, if a drop remains a t the end, then the milk is pure. If, on the other hand, the drop is not found, it may be safely concluded the milk has been adulterated. This is certainly a very simple, and it is said to be a reliable test.” If we are not mistaken we have heard of this test twenty years ago.

ISSN:0003-2654    

DOI:10.1039/AN8881300200

出版商:RSC    

年代:1888

数据来源: RSC