146 Chemistry and Chemical Arts. 
spontaneously, because the purple compound is held in solution by 
the gum. In order to throw it down, alcohol is added of the sp. gr. 
of 0.75, and in the proportion of twice its weight, if carbonate of 
soda has been employed, and three times, if the solution of gold has 
been left acid. ‘The purple is deposited gradually, bringing with it 
a certain quantity of gum; of which it contains the more, in pro- 
portion as more alcohol is employed. In order to give density to 
the purple, it is washed with alcohol, thrown upon a filter and pres- 
sed in bibulous paper. In order to purify it, and to separate the 
muriatic acid it may contain, rub it in a mortar with alcohol of 0.50 
so as to make a clear jelly, after which add largely of alcohol, bring- 
ing the liquid to ebullition for two or three minutes, and then add 
abundance of water, and leave the purple to deposit itself, finally 
washing it with a small quantity of water, in the way of decantation. 
It then contains only a small quantity of gum, which facilitates its 
ultimate use. It is necessary, however to execute the paintings with 
the oil of turpentine, since if water is used, the gum swells up, and 
the action of the fire will produce scales over the surface of the 
painting.— Idem. 
25. New method of producing heat.* (Mem. Encyclo., t. 3. p. 
336.)—-By projecting upon a fire, a mixture of water and oily matters 
in a certain proportion, a flame is produced, whose heat is extremely 
intense. Ifthe water be in excess, the flame languishes; or if in 
too small quantity, a smoke is produced. For 1 measure of tar, it 
is requisite to employ about 14 of water. 15 lbs. of oil of turpentine 
mixed with 15 lbs. of water, and projected upon 25 lbs. of Newcastle 
coal, produced as much heat as 120 lbs. of this coal.—Ann. des 
Mines, t. 5. p. 378. 
26. The best method of assaying the ores of Manganese, by 
Zenneck. (Journ. d’ Erdmann, t. 18, p. 75.)—The principal pneu- 
matic methods are the following: 1. Calcination and measuring the 
quantities of oxygen gas evolved; 2. Ebullition with concentrated 
sulphuric acid and measuring the quantities of oxygen; 3. Calcina- 
nation with sugar, and measuring the volume of carbonic acid form- 
ed; 4. Ebullition with muriatic acid, and measuring the quantity of 
chlorine disengaged; 5. Ebullition with muriatic acid and making 
* Mr. Samuel Morey, long ago detailed similar facts in this Journal.—Ed. 
