270 Maxson — Determination of Small Amounts of Gold. 



Akt. XX. — The Colorimetric Determination of Small 

 Amounts of Gold ; by Ralph Nelson Maxson. 



[Contributions from the Kent Chemical Laboratory of Yale Univ. — cxlv.] 



Application of the colorimetric method for the estimation 

 of small amounts of gold, based upon the purple of Cassius 

 coloration, have been proposed by Carnot,* R,ose,f Sonstadt,^: 

 Cassel,§ Prister,|| Moir"f and others, but the use of this reaction 

 for such a purpose is open to objection. According to the 

 authority of other workers, the coloration thus produced is 

 extremely variable, varying in intensity and shade according to 

 the condition of the solution and precipitant. Moreover the 

 substance is unstable, and artificial standard solutions are 

 necessary if accurate results are to be obtained. 



It has been suggested that the coloration of red colloidal gold 

 suspensions might have a quantitative relation to the amount 

 of metal present and a method of colorimetric estimation, free 

 from the objections stated above, be based upon this relation. 

 The following investigation was therefore undertaken in the 

 hope of discovering whether such a relationship would not 

 offer a suitable means for the estimation of small amounts of 

 gold. 



The preparation of the red colloidal suspensions was natu- 

 rally the first object of interest. Blake** has shown that acety- 

 lene is the most suitable reagent for effecting the reduction of 

 the auric salt, the treatment consisting in drying the chloride 

 at 170°, dissolving in ether, and pouring the etheral solution 

 into water also containing ether and saturated with acetylene 

 gas. The use of ether was objectionable for the purpose of this 

 investigation and the simpler procedure described below gave 

 good results. 



The measured quantity of a standard solution of the auric 

 salt was drawn off into a calibrated flask and treated with a 

 suitable amount of an aqueous solution of acetylene, made by dis- 

 solving the previously washed gas in water distilled and cooled 

 in tin. The color having developed, the solution was shaken and 

 the flask filled to the mark. The gold solutions used in these ex- 

 periments were prepared from pure gold chloride, which con- 

 tained hydrogen chloride in the usual amounts, and had not 

 been subjected to a preliminary drying. The standard of 

 these solutions was determined gravimetrically by means of 

 magnesium ribbon, and by the electrolytic process with the 



* Compt. Bend., xcvii, 105 and 169. fChem. News, lxvi, 271. 



\ Cbem. News, xxvi, 159. § Eng. and Min. Jour., 76, xviii, 661. 



I Jour. Chein. Met. and Min. Soc. of South Africa, iv, 235, 1903. 



•ff Jour. Chem. Met. and Min. of South Africa, Sept. 1903. 



** This Journal, xvi, 381 (1903). 



