216 Scientific Intelligence. 



and the reaction mixture, after dilution to 80 cc , was shaken for 

 24 hours : 



HgCl taken 



AgCl taken 



AgCl in solution 







VI g. 



0-0764 g. 



0003 g. 



or 



0-4 $ 



1-1 " 



0-1527 " 



0-0030 " 



<< 



2-0 " 



1-1 " 



0-2291 " 



0-0054 " 



a 



2-4 " 



1-1 " 



0-3054 " 



0-0448 " 



<< 



14-7 " 



1-1 " 



0-3818 " 



0-0938 " 



a 



24-4 " 



The results show that the method fails when the relative propor- 

 tion of mercurous chloride is large, and that, even when a reac- 

 tion is obtained, it may give no indication of the amount of silver 

 present. The methods that are suggested to replace this unsatis- 

 factory one consist in the oxidation of the chloride mixture either 

 by bromine or by sodium hypochlorite and nitric acid. The lat- 

 ter dissolves the mercurous chloride quickly in the cold. It may 

 be mentioned here that the process employed in the Sheffield 

 Chemical Laboratory for many years consists in treating the mix- 

 ture of chlorides at first with ammonia, and then, if no satisfac- 

 tory reaction for silver is obtained, treating the black residue 

 with a little boiling aqua regia until the black color has dis- 

 appeared, then diluting, filtering, and treating again with ammonia. 

 — Zeitschr. anorgan u. allgem. Chem., xciii, 320. h. l. w. 



3. The Diffusion of Solids. — C. E. Van Orstband and F. P. 

 Dewey have made a preliminary investigation upon this subject. 

 They propose to continue the work and to determine the diffusion 

 for minerals and other solids over a considerable range of tem- 

 peratures and pressures. There is no doubt that the results of 

 such an investigation would be of much interest in connection 

 with geological science. The fact that metallic gold diffuses iDto 

 metallic lead even at ordinary temperatures was observed by 

 Roberts-Austen about 19 years ago. The present paper deals 

 only with the diffusion of these metals and the authors have con- 

 firmed the earlier results as far as the rates of diffusion at some- 

 what elevated temperatures are concerned, but they find a higher 

 coefficient of diffusion at 100° than was found by Roberts-Austen. 

 An example of the results may be given. A lead cylinder with 

 its end in contact with gold for 54 days at 197° C. showed the 

 following percentages of gold at distances ranging from 2 to 24 

 millimeters from the surface of contact, where each distance in- 

 creased regularly to the extent of two millimeters : 0-0187, 0*0145, 

 0-0109, 0-0080, 0-0057, 0'0044, 0-0030, 0-0020, 0*0012, 0-0008, 

 0-0002, 0-0001. It is to be noticed that the gold penetrated into 

 the lead to the distance of about an inch. The authors were 

 unable to detect the penetration of lead into the gold for a dis- 

 tance greater than 0*2 mm , but it is to be observed that the methods 

 for detecting lead in gold are far less delicate than the assay 

 method for finding gold in lead. — U. S. Geol. Survey, .Profess. 

 Paper 95- G. h. l. w. 



