LARD AND LARD ADULTERATIONS. 467 



liquid, or give particles of reduced silver in the liquid or on the sides of 

 the tube.* 



I have employed the following modification of Millian's method, which 

 acts more satisfactorily than the original. 



The re-agents are placed in a round -"bottomed porcelain dish of about 

 50cc capacity. The silver re-agent is acidified by the addition of from .5 

 to Ice of pure nitric acid. The reaction is conducted on a steam bath. 



With the fat acids of cotton oil the order of phenomena is as follows : 



The fat acid being thoroughly dissolved and warmed to the evap- 

 orating point of the alcohol, 2cc of silver re-agent are added and quickly 

 stirred in with a glass rod. An almost immediate deep brown colora- 

 tion is noticed, passing quickly to black. As the alcohol evaporates, 

 the reduced silver collects in mirror-like scales and is carried onto the 

 sides of the dish by the escaping alcohol. In a few minutes the liquid 

 begins to grow clear again, and in ten minutes almost the whole of the 

 reduced silver is attached to the sides of the dish. 



The fatty acids for use in this modification were separated in the 

 summer of 1888, but on account of a stress of other duties the work 

 was not done until in December. The notes of these tests were mis- 

 laid, and in February, 1889, the work was again done. 



The results of the second set of determinations were quite surprising, 

 and lead one to suppose that the fat acids should riot be kept a long 

 while before treatment with the silver solution.! 



In most cases the reactions were quick and satisfactory, but in a few 

 cases entirely misleading. The fat acids of some cotton oils failed to 

 give any reductions whatever, and in some of the mixed lards, where 

 cotton oil was known to be present, the reduction was so slight as to be 

 wholly useless for analytical purposes. My experience with more 

 recently-prepared samples showed that in such cases the anomalies 

 mentioned above are not repeated. With pure lards there was also a 

 trace of reduction noticed in some cases, which I suppose would not be 

 seen in the freshly-prepared samples. The reaction with cottonseed oil 

 acids, when it appeared at all was so clear and unmistakable, as to lead 

 me to believe that in these respects the process of Milliau is an improve- 

 ment on the method of Bechi. In the instances marked " trace of reduc- 

 tion " the separation of a slight amount of a substance was noticed, 

 which, however, was usually of a brown color, and did not resemble in 

 any inaiked degree the intense blue-black mirror-like deposit of silver 

 by pure cotton oil. The use of the terms trace of reduction and slight 

 reduction in 'the tables should not be construed into evidence of the 

 presence of cotton-oil fat acids in the samples so marked. 



The marked and heavy reductions we_re attended by an immediate 

 brown color on adding the re-agent, passing rapidly into black. After 

 heating for a few minutes the silver was deposited as black mirror-like 



* Journal of the Chemical Society, August 31, 1888. 



tThis loss of reducing power in samples of cotton oil long kept has also been no- 

 ticed by other observers, 



