FOOD-COLOEING SUBSTANCES. 3 



The solutions named below are usually dropped from a pipette 

 into tlie solutions under examination. For convenience they should 

 be kept in bottles provided with glass caps ground on an enlargement 

 of the neck. With this form of bottle a short graduated pipette 

 (or piece of tubing) can be kept in the bottle under the cap. The 

 solutions are: 



Bromin water, 1 or 2 per cent. One per cent solution is about 

 fourth-normal as oxidizing agent. 



Hydrazin sulphate solution, 3.2 per cent (approximately normal as 

 a reducing agent when oxidized to water and free nitrogen). 



Sodium nitrite, 7 grams per 100 cc (approximately molecular normal) . 



Alplia-naplithol solution, from 10 to 20 per cent in alcohol. This 

 solution is used in very small quantities and should be kept in a 

 bottle of the same form as used for the other reagents but of smaller 

 size. The solution becomes dark colored and unfit for use after stand- 

 ing some weeks. 



Sodium hydrosulphite solution (NagSgO^, ''Blankite"). This solu- 

 tion is unstable and is best prepared as needed. The writer prefers 

 to use the powdered sohd kept in a small bottle, in the cork of which 

 is fixed a strip of sheet metal to serve as a spatula. With this 

 arrangement the salt, which is very soluble, may be dropped, a few 

 particles at a time, into the solution to be tested. 



Potassium persulphate (KjSgOg) . The same observations apply here 

 as under "Sodium hydrosulphite solution." 



The following reagents should preferably be kept in some form of 

 small dropping bottle: Concentrated hydrochloric acid, concentrated 

 sulphuric acid, dilute hydrochloric acid (10 per cent), sodium hydroxid 

 (10 per cent), ammonium hydroxid (density about 0.95), ferric 

 chlorid (10 per cent), and stannous chlorid (40 grams in 100 cc 

 conwntrated hydrochloric acid). 



Other reagents needed are : Solutions of alum, barium chlorid (or, bet- 

 ter, barium acetate), uranium acetate or uranium sodium acetate, and 

 sodium acetate. It is convenient to have the last-named solution 

 api)roximately normal, 16 grams per 100 cc. A strong solution of 

 lead acetate (normal, not the basic salt, 30 per cent) is used in con- 

 siderable amount; and a rather carefully made 10 per cent sodium 

 carbonate solution (double normal) is useful for separations of 

 Orange I and for coupling reactions. Common salt solution made 

 from C. P. sodium chlorid is useful for many separations. Two 

 hundred and fifty grams per liter is a convenient concentration. 



The following solvents are most frequently used: 



Alcohol. 



Amyl alcohol. This should b<' a good grades of "pyridin-free." 



Gnsoliice or petroleum ether, " lov) boiling point," of density ahout 

 0.G5. Commercial pc^ntane, though expensive, may be prefeiTcd 



