ANALYSES OF CERTIFIED PERMITTED COLORS. 



201 



COMPARISON WITH ANALYSES MADE IN 1907. 



A comparison, as far as possible, of these figures with the corre- 

 sponding data previously given for samples on the market in the 

 summer of 1907 is made in the following table. The figures in this 

 new table show the value of the fraction obtained by dividing the 

 old average figure by its corresponding new average figure that is, 

 they show how many times greater the old average figures are than 

 the corresponding new average figures. Italics indicate those items 

 in wliich there has been a retrogression in the new figures as com- 

 pared with the old; all the other figures represent an advance. It 

 will be noted that comparisons are not made for Ponceau 3B. and 

 Erythrosin. This comparison was omitted because there was but 

 one sample of Ponceau 3E- examined and a partial analysis of one 

 sample of Erythrosin in the old work. 



Ratio of average figures of 1907 to those for the certified colors, 1909. 



These retrogressions are: 



1 . Salt in the Green. 



2. Nonvolatile insolubles in the Yellow. 



3. Nonacid ether extract in the Green. 



4. Nonacid ether extract in the Blue. 



5. Total ether extract in the Blue. 



With respect to the first of these retrogressions there is this to be 

 said: One lot of Green had apparently been purified by precipitation 

 with salt, since it was in every other respect of a high quality that 

 is, it was free from arsenic and heavy metals within the pharmacopceial 

 test, and its ether extractives were very satisfactory. The other lots 

 of Green examined had apparently not been made in this manner. 



With respect to the second retrogression, the probable explanation 

 is that some of the lots were made during a period when the municipal 

 water supply was excessively hard, as before explained. The remain- 

 ing three retrogressions are probably due to the fact that the old 

 methods of analysis used were not so accurate as the methods later 

 employed and hereinafter described (pp. 223, 225). 



It will be noted that in three of the six batches of Indigo disulpho 

 acid reported there is no sodium sulphate; whereas in the other three 

 batches the amount of this substance is as high as 16.12. The reason 

 for this is that in the early stages of the work the results obtained 



