THE ALUMNI JOURNAL. 



87 



German reagent, without heat, and that 

 treated with 1 Cc. of the U. S. P. reagent, 

 metallic tin and heat. The specimens 

 containing less than 2.5 Cc. of reagent 

 showed a less intense color. 



These experiments were repeated with 

 the three solutions containing 0.5 Mgm. 

 As in 1 Cc. and resulted as follows : 



a. With the U. S. P. solution of Sn 

 Cl 2 : — 



i Cc. of reagent gave no reaction dur- 

 ing 45 minutes, then gradual coloration 

 began. If heat be applied the reaction 

 begins in 18 minutes, and at the end of 

 one hour is slightly more intense than 

 when treated without heat. 



1.5 Cc. of reagent : reaction slightly 

 more rapid and intense than with 1 Cc. 



2.0 Cc. of reagent : still more rapid 

 and intense, both with or without heat- 

 ing. 



2.5 Cc. of Sn CI 2 : reaction begins in 

 15 minutes at air temperature, in less 

 than 5 minutes when heated. 



3.0 Cc. of Sn Cl 2 : reaction slightly 

 less intense than with 2.5 Cc, both hot 

 and cold. 



3.5 Cc. of reagent : a still further slight 

 decrease in intensity. 



No difference could be observed in the 

 reaction of As 2 3 and As 2 5 ; the so- 

 dium metarsenite appeared to be very 

 slightly more colored than As 2 3 . 



b. With 1 Cc. of U. S. P. solution and 

 a small piece of metallic tin, at a temper- 

 ature of about 8o° C, 1 Cc. of the solu- 

 tion containing 0.05 Mgm. of As began 

 showing a brownish color at 15 minutes. 

 At 35 minutes the reaction was quite 

 sharp and continued to grow slowly in 

 intensity to the end of the hour. 



No difference was perceptible between 

 As 2 O, and As 2 5 . 



c. 3 Cc. of the solution of the Arznei- 

 buch, mixed with 1 Cc. of the solutions 

 containing 0.05 Mgm. of As began show- 

 ing a feeble reaction at 35 minutes, and 



at the end of the hour, showed a plain 

 reaction, as compared with the unchang- 

 ed solution, but did not equal in intensity 

 the reaction produced by the addition of 

 metallic tin. 



On repeating the experiments with 

 solutions containing o 03 Mgm. of As in 

 1 Cc. a feeble reaction resulted from the 

 use of stannous chloride and metallic tin 

 at the end of an hour, but even after 

 standing over night, the other methods 

 gave such a faint reaction that it requir- 

 ed close inspection in the colorimeter to 

 perceive the change. A solution con- 

 taining 0.02 Mgm. of arsenic failed to 

 show any reaction. So I think that for 

 practical purposes, the utmost limit of re- 

 action is reached at 0.03 Mgm. of As in 

 1 Cc. and that the method employing 

 metallic tin and heat is to be preferred, 

 where the presence of antimony or bis- 

 muth does not forbid its une. Even the 

 addition of pure concentrated sulphuric 

 acid, which was recommended when the 

 test was first introduced, has not yielded 

 to me any substantial advantage in de- 

 tecting the presence of arsenic in the 

 greater dilutions. 



2. THE BEST PROPORTION OF REAGENT 

 TO SPECIMEN. 



In the foregoing experiments and a 

 number of others conducted for that pur- 

 pose, it was observed that both with the 

 U. S. P. solution (without the use of me- 

 talic tin) and with that of the German 

 Pharmacopoeia, the greatest intensity of 

 color obtained after an hour's reaction 

 occurred when 1 Cc. of the arsenical 

 solution was mixed with 2.5 Cc. of the 

 reagent. Between 3 Cc. and 2 Cc. of the 

 German solution hardly any difference 

 could be found. But with the pale U. 

 S. P. solution a very slight difference ap- 

 peared in favor of 2 Cc. as against 3 Cc. 

 Heat did not appear to affect the propor- 

 tion needed. 



When metallic tin was added it seemed 



