232 THE ANALYST. C 0 R R ESP OND EN C‘E. [The Editor is not in any way responsible for opinions expressed by his Correspondents.) To THE EDITOR OF c c T ~ ~ ANALYST.” SIR,-I can bear witness to the ferroc anide test for zinc spoken of by Mr. Allen in thia month’s ANALYST, having used it for some years. $ believe it was shewn me by a friend, who had come across i t in testing a water for iron. 1 am in the habit of applying it directly to the water in the presence of excess of hydrochloric acid, and I believe it is slightly more sensitive in this form than where chloride of ammonium is used in a neutral solution. A solution of zinc was prepared, containing one part in 200,000, with five per cent. of ammonium chloride; after half a minute or so a cloud appeared, the solution was then divided into two parts, and to one of them a little hydrochloric acid was added ; after a further interval it was observed that the latter solution was distinctly the more turbid.On one occasion, having peroxydized iron with pemanganate before using the ferrocyanide test for that metal, I ObBerved, after a short time, a white cloud, which I afterwards found was due to manganese. Since the appearance of Mr. Allen’s paper, I have further investigated this reaction, and b d that in a five per cent solution of chlorideof ammonium it is extraordinarily delicate, astrong and immediate turbidity appearing in solutions.of manganese containing only one part per million. I do not find this test, which seems to be of much value as a negative one, in any of the text-books. Since making my experiments I have looked back through my file of the ChemicaZ Newi? to the original paper of Mr.Allen, and I find that there he mentions ferrocyanide as a test for manganese, but the precipitate in that caee is a ooloured one, and he gives no data as to delicacy. I think, therefore, that my observation is worth recording. Yours, $0.’ Shrewsbury, November 8th, 1884. THOMASP. BLUNT. To TEE EDITOR OF “TRE ANALYST.” SIR,--In the extract on the L c Determination of Arsenic,” given in THE ANAZYBT for November, In the example given the amount of As, 0,’ taken for the experiment, is stated to be 0.1814 p., If, as would appear, the iodine solution were decinormal, the corresponding amount of As,O, The 38-9 0.0. iodine solution is given as equal to 0.1323 gmn., oompared with 0.1330 required by %culating the arsenic the quantities would be 0*1458 Aa.found and 0.1374 required by theory, there is evidently a misprint, and the amount of iodine solution required for the final titration is given as 38.9 C.C. would be 9.1925 grm., theory requiring 0.1814. the0 Southampton, November loth, 1884. I: am, yours, &c., J. BRIERLEY. To THE EDITOR OF “TEE ANALYST.” SIa,-Having in the practice of my profession observed that exhibitors of unpatented inventions, a t International and Industrial Exhibitions, are not generally aware that their position is affected by certain provisions of the c 4 Patents, Designs, and Trade Harks Act, 1883.” I beg to point out through the medium of your paper that the six months’ protection of Inventions so exhibited is no longer accorded unconditionally, such protection being now obtainable only b compliance with the requirements stated in Section 39 of the above mentioned Act, and Rule 17 of the Jatents Rules.Details of the mode of procedure may be obtained from the proper official souroet of information, without charge, on application. I am, Sir, your obedient servant, W. T. WHITEMAN, Fellow of the Institute of Patent Agents. BOOKS, &c., RECEIVED. Aids to Public Health, by J. L. W. Thudichum ; The Assay and Analysis of Iron and Steel, by Thomas Bayley; Inorganic Chemistry, by B’rankland and Japp; Report (forty-secmd) of the Legislature of Massachusetts relating to the Registry, edited. by Frank Wells, N.D. ; Statutes of Massa- ohusetts, relative to the adulteration of Food and Drugs ; Tablets of Chemical Analysis, by Armand Semple ; American Druggidi; The American Garden ; American Grocer ; The Brewers Guardian ; British Amercan Journal ; The Chemist and Dru gist ; The Cowkeeper and Dairyman’s Journal ; The Grocer ; The Grooers’ Gazette; Independent Journa?; Invention and Inventors’ Mart; The Lancet ; The Medical Becord ; Medical Press and Circular ; The Pharmaceutical Journal ; Ban Francisco News &etter ; Science Monthly ; Scientific American.