418 Dr. J. H. Long on the 



n KI required 1*37 e.c. ^AgNOg per hour = 0-1364 gr. KI in 24 hours. 



wNal „ 1-12 „ „ „ =0-1008 „ Nal „ 



wNaBr „ 0-85 „ „ =0-0525 „ NaBr „ 



nKCj „ 0-64- „ „ „ =0-0499 „ KCy ,. 



The last value can be considered only an approximation 

 to the truth, as the cyanide contained a little cyanate, and, 

 besides, in solution it suffers always more or less decompo- 

 sition, 



Diffusion of Nitrates , 



The first difficulty in connexion with these salts was the 

 accurate determination of the small amounts diffused. This 

 was finally accomplished, however, by means of the " Marx " 

 method, which, as is well known, depends on the decoloration 

 of a solution of indigo by free ffiSr0 3 . 



An indigo solution was prepared as recommended by Marx*, 

 and was of such strength that 8 cubic centims. corresponded 

 to 1 milligram N0 3 . The liquid containing diffused salt was 

 evaporated to a small volume and 25 cubic centims. taken. 

 To this were added 50 cubic centims. concentrated H 2 80 4 , and 

 the indigo was run in immediately from a burette. If more 

 than 30 cubic centims. of this were required, the operation was 

 repeated with a weaker liquid. By means of this preliminary 

 titration it was possible to determine approximately the amount 

 of N0 3 in the solution to be examined. This should not contain 

 more than 4 or 5 milligrams in 25 cubic centims. The first test 

 was soon found to be unnecessary, however, as a few titra- 

 tions showed about how much salt was to be expected for a 

 certain number of hours. Then, by making two titrations, 

 the first a near approximation, it was possible to obtain pretty 

 accurate results. Enough solution was always taken to require 

 from 30 to 50 cubic centims. indigo solution. Observing these 

 precautions, the following experiments were made: — 



Diffusion of | BalS^ 6 . 



Diffusion of | SrN 2 6 . 



Time. 



Amount diff. 



Time. 



Amount diff. 



8-12 



•0068 g 



ram. 



6-10 A.M. 



•0204 gram. 



12-6 



•0110 



v 



10-6 



•0090 „ 



6-12 A.M. 



•0315 



v 



6-12 A.M. 



•0211 „ 



12-6 



•0107 



j) 



12-6 



•0076 „ 



6-12 A.M. 



•0330 



jj 



6-12 A.M. 



•0229 „ 



52 hours. 



•0930 





6Q hours. 



•0810 „ 



* Fresenius' Zeitschrift, vii. p. 412. 



