FOOD-COLORING SUBSTANCES. 6 
The solutions named below are usually dropped from a pipette 
into the 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) . 
Alpha-naphthol 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 (Na 2 S 2 4 , "Blankite"). This solu- 
tion is unstable and is best prepared as needed. The writer prefers 
to use the powdered solid 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 (K 2 S 2 8 ) . 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 
concentrated 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 
approximately 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 be a good grade of a pyridin-free.' ; 
Gasoline or petroleum ether, "low toiling point," of density about 
0.65. Commercial pentane, though expensive, may be preferred 
