The Cowkeeper and Dairyman's Journal says:-" A defendant, rejoicing in the appropriate name of Simpson, has been fined by the Belper magistrates for having too liberally diluted a large quantity of milk intended for the London market. Though the water supply of the metropolis is by no means adequate to the requirements of the population, yet it is not at all desirable that water should be sent to us in milk cans from Derbyshire. We are glad, therefore, that Mr. Simpson has to pay heavily for his attempt to do a service in this respect. The milk which he proposed to pass off upon the confiding public of the metropolis as a genuine bovine extract was proved on analysis to contain 23 per cent. of water. He had no defence to make for having thus attempted to cheat his customers, and accordingly pleaded guilty to the offence with which he was charged. Considering that the London purveyors of milk add plenty of water to it after it arrives here, the dairy farmers who send it up from the country should be all the more careful to despatch it in an unadulterated condition. We trust that other enterprising dairymen of the 'Simpson' class will take warning from the treatment he has deservedly received at the hands of the administrators of justice at Belper."

Mr. William Morgan, Ph.D., of Swansea, has been appointed Public Analyst for the town and county of Haverfordwest.

ERRATUM.-On page 7 of our last number, line four, "Proposed Draft of a National Act," should have been "Abstract of Proposed Draft," &c., as only the principal clauses are there set out.

RECENT CHEMICAL PATENTS.

The following specifications have been recently published, and can be obtained from the Great Seal Office, Cursitor Street, Chancery Lane, London.

The Chemist and Druggist; The Brewers' Guardian; The British Medical Journal; The Medical Press; The Pharmaceutical Journal; The Sanitary Record; The Miller; Journal of Applied Science; The Boston Journal of Chemistry; The Provisioner; The Practitioner; New Remedies; Proceedings of the American Chemical Society; Le Practicien; The Inventors' Record; New York Public Health; The Scientific American; Society of Arts Journal; Sanitary Engineer of New York; The Cowkeeper and Dairyman's Journal; The Chemists' Journal; Oil and Drug News; The Textile Record of America; Sugar Cane.

THE ANALYST.

MARCH, 1881.

35

SOCIETY OF PUBLIC ANALYSTS.

AN EXTRAORDINARY GENERAL MEETING was held on the 16th February last, at Burlington House, Piccadilly.

Mr. Heisch, on taking the chair for the first time as President, thanked the Members for the honour they had done him in electing him to that position, and apologized for his absence at the Annual Meeting on account of being snowed up at Croydon, and the telegraph wires being also broken he could not communicate with the Secretary.

The Requisition for the Meeting having been read, Dr. Bartlett proposed, Dr. Tripe seconded, and it was unanimously resolved that the following be an additional Rule of the Society:"That in the event of the resignation or death of any Officer, or of the voting by ballot for the election of an Officer of the Society resulting in an equality of votes, it shall be in the power of the Council to declare the office vacant, and to fill it up for the remainder of the current year, at their first Meeting after the date of such occurrence." An ordinary General Meeting was then held.

The minutes of the Meeting having been read, were confirmed.

Dr. Bartlett and Mr. Maxwell Lyte having been appointed Scrutineers, opened the ballot papers, and reported that the following gentlemen were duly elected Members of the Society :-Thomas Stevenson, M.D., F.C.S., F.I.C., of Guy's Hospital, Public Analyst for Bedfordshire, Surrey, &c.; Horace Swete, M.D., F.C.S., Public Analyst for Worcester, &c.; W. Douglass Hogg, M.D., F.S.P., Chemist, of Paris; P. Vieth, Ph.D., F.C.S., Analytical Chemist; H. J. Yeld, M.D., F.C.S., Public Analyst for Sunderland; W. Johnstone, F.C.S., F.I.C., Public Analyst for King's Lynn; J. J. Broadbent, F.C.S., Analytical Chemist, of Charing Cross Hospital.

Letters were read from Prof. Fresenius and Dr. Hoffman accepting the Honorary Membership of the Society, and were ordered to be entered on the minutes.

The following were proposed for election and will be balloted for at the March Meeting. As Members-W. D. Sykes, M.D., Public Analyst for Portsmouth; John Parry, Public Analyst for Penryn; Henry Liepmann, Ph.D., F.C.S., Analytical Chemist, Leadenhall Street, London. As Associates-W. Fox, Assistant to Mr. J. Baynes, of Hull, and D. A. Sutherland, Assistant to Dr. Drinkwater, of Edinburgh.

The following papers were then read:-"On a Simple and Expeditious Process for Determining Nitrates and Nitrites in Water Analysis," by M. Whitley Williams.

"On the Action of Permanganate on Potable Waters at Different Temperatures,' by G. W. Wigner and R. H. Harland.

The next meeting of the Society will be held at Burlington House on Wednesday, the 16th March.

A SIMPLE AND EXPEDITIOUS PROCESS FOR THE ESTIMATION OF NITRIC ACID IN WATER ANALYSIS, WITH SOME REMARKS ON THE

ESTIMATION OF NITROUS ACID.

BY M. WHITLEY WILLIAMS, F.I.C., F.C.S., formerly Chemical Assistant in the Royal Institution of Great Britain.

Read before the Society of Public Analysts on 16th February, 1881.

It is well known that when zinc is immersed in copper sulphate solution it becomes covered with a spongy deposit of precipitated copper. If the solution of copper sulphate be sufficiently dilute, this deposit of copper is black in colour and firmly adherent to the zinc. It is, however, not so generally known that the zinc upon which copper has thus been deposited possesses the power of decomposing pure distilled water at the ordinary temperature, and that it is capable of effecting many other decompositions which zinc alone cannot. Among these is the decomposition of nitrates, and the transformation of the nitric acid into ammonia. Messrs. Gladstone and Tribe have shown that the action of the " 'copper-zinc couple" (as they call the conjoined metals) upon a nitre solution consists in the electrolysis of the nitre, resulting in the liberation of hydrogen and the formation of oxide of zinc. This hydrogen is liberated upon and occluded by the spongy copper, and when thus occluded it is capable of reducing the nitre solution in its vicinity. The nitrate is first reduced to nitrite of potassium, and the nitrous acid is subsequently transformed into ammonia by the further action of the hydrogen. In a paper lately read before the Chemical Society I have shown that even in very dilute solutions of nitre the nitric acid can be completely converted into ammonia in this manner with considerable rapidity; and I have further shown that the reaction may be greatly hastened by taking advantage of the influence of temperature, acids, and certain neutral salts which increase the electrolytic action of the couple. I there showed that carbonic acid-feeble acid as it is-suffices to treble the speed of the reaction, and that traces of sodium chloride (0·1 per cent.) accelerated it nearly as much as carbonic acid. A rise of a few degrees in temperature was also found to hasten the reaction in a very marked degree. The presence of alkalies, alkaline earths, and salts having an alkaline reaction, was found to retard the speed of the reduction.

Upon those experiments I founded a simple and expeditious process for estimating the nitric and nitrous acid in water analysis, which, when used with skill, may be applied to by far the greater number of waters with which the analyst is usually called upon to deal. Before describing this process I will first say a few words upon the nature and use of the copper-zinc couple, about which considerable misapprehension appears to exist even in the best informed quarters. This appears very plainly from the description of the copper-zinc couple process given in the Handbook of Water Analysis, recently published by Frankland, in which mistaken directions are given for making the couple and applying it to the estimation of nitric acid in water analysis. There are two kinds of copper-zinc, one (the "dry couple") intended for anhydrous reactions, the other (the "wet couple") intended for hydrogenizations in watery or alcoholic solutions. These two are quite different reagents, differently prepared and different in their application. It is the "wet couple" alone which is adapted to bydrogenizations, such as the transformation of nitric acid into ammonia; but in the handbook

referred to, the dry couple is described as being used for effecting this transformation, a purpose to which I believe it has never been applied, and for which it would certainly be very inefficient.

The wet couple, with which alone we have now to deal, is prepared in the following manner :-The zinc to be employed should be clean, and for the sake of convenience should be in the form of foil or very thin sheet. It should be introduced into a flask or bottle, and covered with a solution of copper sulphate, containing about 8 per cent. of the crystallized salt, which should be allowed to remain upon it until a copious firmly adherent coating of black copper has been deposited. This deposition should not be pushed too far, or the copper will be so easily detached that the couple cannot be washed without impairing its activity. When sufficient copper has been deposited the solution should be poured off, and the conjoined metals washed with distilled water. The wet couple is then ready for use.

To use this couple for the estimation of nitrates, in the manner I am about to describe, it should be made in a wide-mouthed stoppered bottle. After washing it is, of course, soaked with distilled water; to displace this, it is first washed with some of the water to be analysed, and the bottle filled up with a further quantity of the water. The stopper is then inserted, and the bottle allowed to digest in a warm place for a few hours. If the bottle be well filled and stoppered, the temperature may be raised to 30° C., or even higher, without any fear of losing ammonia. The reaction will then proceed very rapidly; but if it be desired to hasten the reaction still more, a little salt should be added (about 0·1 grm. to every 100 c.c.), or if there be any objection to this, the water may have carbonic acid passed through it for a few minutes before it is poured upon the couple. In the case of calcareous waters, the same hastening effect may be obtained, and the lime may at the same time be removed by adding a very little pure oxalic acid to the water before digesting it upon the couple. In my paper communicated to the Chemical Society I showed that nitrous acid always remained in the solution until the reaction was finished. By testing for nitrous acid the completeness of the reaction may be ascertained with certainty, and perhaps the most delicate test for nitrous acid that can be applied for this purpose is that of Peter Griess, in which metaphenylene diamine is the reagent employed. When a solution of this substance is added to a portion of the fluid, and acidified with sulphuric acid, a yellow colouration is produced in about half-an-hour if the least trace of a nitrite be present. The reaction easily detects one part of nitrous acid in ten millions of water. When no nitrous acid is found, the water is poured off the couple into a stoppered bottle, and, if turbid, allowed to subside. A portion of the clear fluid, more or less according to the concentration of the nitrates in the water, is put into a Nessler glass, diluted if necessary, and titrated with Nessler's reagent in the ordinary way.

This process may be used for the majority of ordinary waters-for those that are coloured, and those that contain magnesium or other substances sufficient to interfere with the Nessler reagent, a portion of the fluid poured off the couple should be put into a small retort and distilled with a little pure lime or sodium carbonate, and the titration of the ammonia performed upon the distillates.

About one square decimetre of zinc should be used for every 200 c.c. of a water containing five parts or less of nitric acid in 100,000. A larger proportion should be used with waters richer in nitrates. The couple, after washing, may be used for two or three

waters more.

When either carbonic or oxalic or any other acid has been added to the water, a larger proportion of Nessler reagent should be employed in titrating it than it is usual to add. I have found 3 c.c. to 100 of the water sufficient in almost all cases.

In calculating the amount of nitric acid contained in a water from the amount of ammonia obtained in this process, deductions must of course be made for any ammonia pre-existing in the water, as well as for that derived from any nitrous acid present.

To ascertain the amount of nitrous acid in a water, Griess's latest method should be adopted. A one-half per cent. solution of metaphenylene diamine in very dilute sulphuric acid should be prepared, and a dilute sulphuric acid containing one volume of oil of vitriol to two volumes of water. One c.c. of each of these solutions are added to 100 c.c. of the water in a Nessler glass, and the yellow colouration produced (if any) is imitated by means of a standard solution of potassium nitrite with the same reagents. This standard solution is prepared from silver nitrite, prepared by precipitation, and re-crystallized from boiling water. A weighed amount of this pure dry silver nitrite is dissolved in boiling water, decomposed with a slight excess of potassium chloride, and diluted to a convenient strength. The solution I usually employ contains 01 of a milligramme of NO, in 1 c.c. A solution of ten times this strength is kept in stock in bottles quite filled and tightly stoppered, and is diluted when required for use. To ensure accurate results the solutions to be compared should be simultaneously started and allowed to stand at least twenty minutes before their tints are compared. They should be at the same temperature, for I have observed that the colouration is developed much more rapidly in warm than in cold solutions. There are other conditions which affect the rate of development of the colouration, but these appear to be of a chemical nature and not easily controlled. In these cases only the final tints of the solution should be regarded. The lengthy time required for the full development of the colour, renders it difficult or at least laborious to prepare a solution of exactly the same tint as that under analysis, and it is therefore desirable to adopt some method of making the titration, which, while sufficiently accurate, shall dispense with the necessity for making a long series of trials. I have usually effected this with the aid of Nessler glasses made from pieces of stout glass tubing, about 30 mm. bore and 200 mm. long, ground at the edges and closed at one end with a glass plate cemented on with Canada balsam. The tubes are of exactly equal bore and are graduated from end to end in millimetres. They are used in the following manner: The solution to be titrated and the test solution are made in the usual way, both columns of fluid being of equal length. The test solution is made as nearly as can be guessed to equal in tint that to be titrated. Usually one will be somewhat deeper than the other; the height of the deeper solution is read off upon the millimetre scale, and a portion of it withdrawn by means of a pipette until the shortened column is equal in tint to the other, when its height is again read off. The amount of nitrite in the shortened column is taken as being equal to that in the other glass, and a simple proportion will give the amount of nitrous acid contained in the solution titrated. In this way the titration can be made very expeditiously.

The metaphenylene diamine solution should be decolourized with animal charcoal whenever necessary.

Dr. Dupré said he was very glad that Mr. Williams had given them the paper and hoped