substance, which gives no reaction for acid or basic coal-tar dye, 

 tests should always be made for caramel. It is best not to depend on 

 any one procedure but to apply several of the many suggested for 

 this purpose. The following have been found most useful: 



Marsh's test as modified by Tolman, depending on the insolubility 

 of caramel color in amyl alcohol. (Bui. 122, Bureau of Chemistry, 

 p. 206.) 



The fuller's earth test is very useful as a supplementary test, but 

 it is first necessary for the analyst to experiment with the particular 

 lot of fuller's earth used. For instance, in the case of vanilla extracts 

 preliminary experiments should be made with known samples of 

 pure extracts and samples colored wholly or partly with caramel. 



Phenylhydrazine test (for extracts). (Bui. 65, Bureau of Chem- 

 istry, p. 71.) 



Paraldehyde test (for distilled liquors). (Bui. 107, Bureau of 

 Chemistry, p. 101.) 



To detect mineral pigments or to identify color lakes, it is neces- 

 sary to examine the incinerated substance for heavy metals, chiefly 

 aluminum, tin, and iron. 



METHODS OF MORDANTING WOOL. 



Mordanting wool with alum. In 500 cc of water dissolve 1 gram of 

 crystallized aluminum sulphate and 1.2 grams of cream of tartar. 

 Stir 10 grams of fat-free wool in the solution for one-half hour, let 

 stand two to three hours, wring and dry at room temperature. 



Mordanting wool with tin. In 500 cc of water dissolve 0.8 gram of 

 tin crystals, and 0.4 grams of oxalic acid. Boil 10 grams of fat-free 

 wool one and one-half hours in this solution. 



Mordanting wool with bichromate of potash. Place 10 grams of wool 

 in 500 cc of water and heat to boiling, then add 0.2 gram of potassium 

 bichromate, 0.35 gram of cream of tartar, and 0.1 cc of concentrated 

 sulphuric acid, and boil one and one-half hours. Dry at low tempera- 

 ture and keep mordanted wool from exposure to light. 



. [Cir. 6:?] 



