﻿34 INDIANA UNIVBESITY 



a variety of peptone. Analyses of some samples of ghie and 

 g'elatine show : 



Per cent 

 of Gelatine. 



"Gelatine" 70.95 



Superior glue 51.98 



Common glue 23.71 



Any decomposition of gelatine or glne by ferments or acids forms 

 gelatin-peptones or gelatones. From the fact that the purest gela- 

 tine for bacteriological nse sho^^'ed a less favorable effect upon the 

 lead deposits than a low grade commercial glue, the conclusion was 

 drawn that some impurity in the glue was responsible for the good 

 result. Glue which had been warmed for several hours with perchlo- 

 ric acid to form gelatin-peptone was tried. The results were un- 

 certain — sometimes good, but more often bad. Acting along the 

 line of this theory, meat peptones were tried. Two different brands 

 of these meat peptones were used — Wittes', probably the purest to 

 be obtained, and a commercial sample from ^Merck, which was five 

 years old and badly decomposed. Both gave approximately the 

 same results, consequently Wittes' peptone was used on account of 

 its greater convenience and lack of foul odor. Experiments showed 

 that about 0.03 to 0.05 gram of this peptone per 100 cc. of solution 

 was required. This ciuantity should be renewed after four or five 

 days, in other words, after the passage of about 25 ampere-hours 

 per 100 cc. of solution. An excess of the peptone did not have any 

 bad effect. The baths did not become ill-smelling even after long 

 runs. There is some material present in or formed from the pep- 

 tone which separates as a pale yellow flocculent precipitate. This 

 precipitate is not alw^aj^s formed, and the conditions for its produc- 

 tion are not known. The presence of this precipitate does not inter- 

 fere with the working of the bath in any way. 



Experimental Data. The current yields are near to the theo- 

 retical, as shown bv the following: table: 



drams of 

 Cu in 

 Coulometer. 



Amperes 



per 

 Sq. Dm. 



Volts. 



Cathode. 



Anode. 



Grams Lead 

 Deposited. 



Yield 

 Per cent. 



Grams 

 Lead 

 Dissolved. 



Ampere 

 EflBciency 

 Per cent. 



4.6475 



2.8 



0.2 



15.1526 



99.77 



15.3111 



100.15 



1.2350 





0.23 



4.0277 



99.8 



4.0838 



101.1 



0.7290 



1.3 





3.3735 



99.6 



3.4134 



101.3 



1.4283 



2 



08 



4.6580 



99.8 



4.7027 



100.7 



1.2054 



1.4 



0.2 



3.7346 



99.6 



3.9656 



100.7 



1* Allen, Commercial Organic AnalpsiSj IV, 479 (1898). 



