Chemistry and Physics. 463 



while the liquid is rapidly cooled. The liquid is then filtered, 

 preferably through asbestos, and the precipitate is washed with 

 cold water. The filtrate is treated with some dilute sulphuric 

 acid and a small excess of standard silver nitrate solution is 

 added. Then the iron is titrated with potassium permanganate 

 solution in the usual way. When the end point has been reached 

 the color of the permanganate is removed by the addition of a 

 trace of ferrous sulphate, and the excess of silver in the solution 

 is at once determined by means of standard ammonium thio- 

 cyanate solution. The iron is calculated in the usual way from 

 the amount of potassium permanganate used, while the copper 

 is calculated from the amounts of ammonium thiocyanate and 

 silver nitrate employed. The test analyses given by the author 

 show remarkably accurate results, and the process seems to be a 

 rapid one. It appears to the reviewer that there are possibilities 

 for errors in this method, if improperly carried out, in the oxida- 

 tion of the ferrous sulphate by the nitric acid introduced, and in 

 the oxidation of silver thiocyanate acid by the permanganate. — 

 Jour. Amer. Chem. Soc, xxxviii, 884. h. l. w. 



3. Colorometric Determination of Acetylene and its Applica- 

 tion to the Determination of Water. — E. K. Weaver has devised 

 a method for the determination of small amounts of acetylene. 

 It is based upon the color produced by allowing a gas containing 

 the substance to pass through an absorbing liquid containing a 

 little cuprous chloride, hydroxylamine hydrochloride and gelatine 

 dissolved in a mixture of alcohol and ammonia. The color is 

 compared with a standard solution of red dye or with a piece of 

 ruby glass. For the details of the apparatus used, which is some- 

 what complicated, reference must be made to the original article. 

 The method is very sensitive, and amounts of acetylene as small 

 as 0*03 mg. may be detected, while amounts up to 2 mg. may be 

 determined with an error of less than - 05 mg. It was the main 

 object of the investigation to devise a method for determining 

 small amounts of water in volatile organic liquids and other 

 things by its reaction with calcium carbide, but the results in this 

 direction were unsatisfactory. However, a qualitative test for 

 water, sensitive to less than - l mg., may be easily made in this 

 way. — Sci. Paper, U. S. Bureau of Standards, No. 267. 



h. l. w. 



4. A Delicate Test for Copper. — W. G. Lyle, L. J. Curtman 

 and J. T. W. Marshal have investigated a reaction, which had 

 been observed by Kudielka several years ago. It is based upon 

 the insolubility of the copper salt of a-amino-n-caproic acid, 

 CH 3 (CHJ 3 CHNH 2 COOH. A solution of this acid was prepared 

 by dissolving Q-Q1 g. of the acid in 100 cc of water. Since free 

 mineral acids interfere with the test, it is best to add some sodium 

 acetate in making it. The precipitate is grayish blue, and the 

 reaction is exceedingly sensitive, and as little as 0*004 mg. of cop- 

 per in a volume of 3 C0 can be detected with certainty. Mercury 

 and zinc are the only other common metals which yield a pre- 



Am. Jour. Sci. — Fourth Series, Vol. XLI, No. 245. — May, 1916. 

 32 



