THE ANALYST. 193 NOTE ON .4 SIMPLE METHOD FOR ESTINATING THE VALUE OF TION I N MILE AND SIMILAR ORGANIC SOLUTIONS. By DR. MUTER, F.C.S. Rsad defore the Society of Pu6lic Analysts, at Bwlington Bouse, on 17tJt January, 1877. BEING called upon to estimate the purity and value of several samples of commercial Salicylic Acid, and not having seen any process as yet published for that purpose, I was led to adopt the following colorimetric method, by which I find it possible to detect and correctly estimate *1 millegram.A standard solution of pure acid; (2) A weak solution of neutral ferric chloride ; and (3) the usual tubes and burette as used for nesslerizing. Some of the purest commercial acid obtainable is first perfectly purified by dialysis and recrystallieation, and the pure and bold crystals thus obtained, are kept for use, after properly drying. Oxe grm.of the chemically pure acid is dissolved iI; a litre of 'water, and a solution is thus obtained, each C.C. of which represents one millegram of Salicylic Acid.% 2. The Azdicator is a very weak solution of pure neutral ferric chloride, of such a strength, that 1 C.C. added drop by drop to 50 C.C.of bhe standard acid, just ceases t o give any increase in intensity of colour before the addition of the last drop or two. One grm. of the commercial sample (after well mixing) is dissolved in 1 litre of water, and 50 C.C. is put into one of the nessler tubes. To this, 1 C.C. of the ferric solution is added, and the colour observed after standing for five minutes. As many C.C.of the standard acid as may be judged necessary are introduced into another tube, made up to 50 C.C. with water, and the 1 C.C. of ferric chloride added. I f after five minutes the colours agree, then the experiment is finished, if not, it must be tried again exactly like nesslerizing. The number of C.C. of standard acid used indicates of course the real amount of Salicylic Acid present in the sample. The colour deepens very distinctly indeed for each & C.C.of the standard acid. To ensure perfect success, all mineral acids must be practically absent. ?he colour is affected at first by the presence of snzall quantities of acetic acid, but by standing for ten minutes instead of five it recovers itself. I am now experimenting to see what substances affect the colour, and hope to be able t o give a full list shortly, but in the meantime I find that the presence of neutral mineral salts generally does not interfere, provided they are such as have no action on the iron.The presence of certain albumenous bodies, notably casein, and the soluble ttlbumenoid of milk causes the colour to become reddish and bad for estimation, but these can be thoroughly eliminated as hereafter described.Betectioiz of Salicylic Acid in Milk, Beer, &c. The march of chemistry has caused quite a trade to spring up in tasteless antiseptics, which may be added t o milk, (hitherto COMMERCIAL SAMPLES OF SALICYLIC ACID AND ITS DETEC- The necessary appliances are ; (1) 1. Preparation of the Standard A c i d . 3. The process.*Note.-When intended for use in the analysis of milk, this solution had better be made in grains, (i.e.) 10 grains in 10,000 grains water.194 THE ANATAYST. without detection) so as to cause it to keep sweet for a day or two. The two articles at present sold for that purpose are Salicylic and BoraciG Acids, and the quantities added are, of course, so minute as not to appreciably affect the total solids.I have found that both may be easily separated from the milk by dialysis, and then made manifest. I n the present paper I have taken the Salicylic Acid first, and leave the detailed considera- tion of the boracic acid till a future meeting, as although I can quditativeZy prove its presence by dialpis; I have not yet succeeded in finding a process of even approximate estimation sufficiently delicate and convenient for the small traces with which we have to deal.To proceed therefore with the former antiseptic :-I take four ounces of the milk or beer and dialyse for twelve hours on a pint of distilled water, at the end of that time I take half-an-ounce o u t from the dialysed liquid, place it in a narrow tube, add a little of the ferric chloride solution, and look down over white paper, if no violet colour be produced, the milk is pure, but if it be tinged, then the dialysis is t o be continued for 48 hours.I n practice, I find that working with the usual small quantities added to milk, 48 hours is sufficient t o fairly equalise the amount of acid, both inside and outside the dialyser, so that on taking a portion for estimation, and calculating to the total amount of fluid, I have never got back less than 86’per cent.of what I put in, even under the worst circumstances. I f the presence of the acid be proved, and an attempt at estimation thus rendered necessary, four ounces of pure milk should be put on to dialyee, so as to give a comparison liquid. This is required because if the milk in the dialyser should go very sour, the colour with ferric chloride will be rendered more reddish, and will not be fairly comparable with the standard. The estimation is to be conducted by the colorimetric method already described, using instead of distilled water, the dialysed fluid from the pure milk or beer.I cannot say at present exactly the degree of accuracy I can claim for the quantitative process as I have not yet experimented in hot weather, or with a great variety of parchment papers, but I may say that I have up till the present got back, as a rule, from 50 to 60 per cent.of the acid put in, after 24 hours, and about 90 per cent. in 48 hours. I n the meantime the process is excellent from a qualitative point of view, while it can be said in favour of the estimation, that at all events the quantity cannot be over stated, and that is an important point for public purposes.Dr. Duprk remarked that the question whether the addition of salicylic acid to milk is, or is not to be looked upon as an adulteration, is one which cannot be decided off -hand. On the one hand, assuming that such addition really preserves milk, some milk becomes valuable, which would otherwise have been lost ; the public is so far a gainer.On the other hand, assuming the efficiency of salicylic acid, it will enable the dairy- man to carry on his business in a more slovenly and careless manner. He was of opinion that the chief cause of the early turning of milk was carelessness in washing out or scouring vessels which were to hold the milk.Cleanliness is at present essential in every part of adairy, but with the use of salicylic acid, this becomes more or less unnecessary, and sweet milk would be no longer a guarantee that the dairy is cleanly conducted; on this account, he felt strongly inclined toolook upon the presence of salicylic acid in milk as an adulteration. Be this however, as it may, the Society was greatly indebted to Dr.Muter for giving a ready means for its detection and estimation. Dr. Bartlett, who was not present during the reading of the first portion of the paper, observed that he was delighted-to hear that progress had been made in the detec-TI33 BNAZYBT. 195 tion and possible estimation of borack and salicylic acids in milk. He had erlcbuntered both during his somewhat large expntence of different samples of milk, re presenting over 4,000 gallons daily.When either of these acids is UELRd in minute quantities only, it is slightly antiseptic, and prevents for some short time the further development of lactic acid ferment germs. If, howewy, the germs are present in large quantities, or are derived from that advanced growth proceeding from the vigourous lactous tbrmen- tation, often taken up in the use of uncleansed utensils, neither boracic nor salicylic acids is able to stop the rapid incressse of acidity, even if employed in large proportions The more minute quantities are, therefore, more to be suspected. Dr.Muter’s plan of dialyais appears admirably suitable for the separation of the serum of the milk from the aolids, so that the solution of salicylic salts may be concen- trated, until it gives the well-known characteristic reaction of forming an inky- blue precipitate with peradts of iron, the colour disappearing on the addition of free hydr ochloric acid. I n reply to a question from Dr. Muter, Dr. Bartlett replied that he was only acquainted with one delicate test for boracic acid, and that was by forming nitride of boron, which gives a pewliar colour reaction to G solution of sulph-amido-benzoio acid,