GENERAL NOTES 127 



and subsequent blacking by treatment with 

 ammonia, sodium sulphite, or other agents. 

 I had long used them all with very unsatis- 

 factory results as to permanence, when I saw 

 this formula in the aforementioned journal 

 and tried it, with such success that I have 

 had no wish to make any change. It always 

 works satisfactorily and I have never had a 

 negative change in any manner after its 

 application. It consists of two solutions, 

 which may be used repeatedly without appa- 

 rent exhaustion. I renew them occasionally, 

 say once or twice in a year, more from habit 

 than necessity, as the old solutions appear to 

 act quite as well as fresh ones, though rather 

 more slowly. The formula is as follows, to 

 be put in two bottles: 



A 



Mercury bichloride 96 grs. 



Potass, bromide 96 grs. 



Water, distilled 12 ozs. 



B 



Potass, cyanide, chem. pure .... 90 grs. 



Silver nitrate 96 grs. 



Water, distilled 12 ozs. 



Shake well and allow to settle ; keep the pre- 

 cipitate cyanide of silver always at bottom 



