MISCELLANY. 
171 
Oxalic acid causes the deutoxide to pass immediately to the state of 
protoxide, but does not alter minium in the least; which is at the same 
time a good mode of purification, and characteristic of minium. Since 
this acid, as well as the proto-nitrate of mercury, and sulphuric acid, re- 
duce the deutoxide to protoxide, and do not affect minium, it may hence 
be inferred, not only that minium is a compound of the two oxides, but it 
is also endowed with a remarkable stability. 
Ann. de Chim, et de Phys. 
Note on the Preparation of Tannin. By M. Duval. — To prepare tan- 
nin by our process, take, as in the usual mode, equal weights of nut galls 
and of ether. Expose these two substances in a glass or stone ware ves- 
sel, to a temperature of 15° or 20°, C; after macerating for one month, 
the mixture having become a somewhat solid paste, place it in a strong 
cloth and submit it to pressure. The product obtained will be of the con- 
sistence of molasses, very adhesive to the touch, and does not disengage 
any portion of the ether which it contains at ordinary temperatures. Jf, 
having placed this mixture in an open vessel, we expose it to the sun, or 
in a stove, at the end of some time we will perceive the surface to become 
covered with efflorescence, while the rest of the mass maintains the 
appearance of a thick honey-like liquid, for more than six months. 
To obviate this inconvenience, which retards the preparation of tannin, 
and affects its purity, by the deposition of foreign bodies contained in the 
atmosphere, it is necessary to submit the mixture to the action of an 
elevated temperature, of at least 120°, C. This temperature may be 
obtained in a very fixed manner, by means of a very concentrated solu- 
tion of chloride of calcium. The chloride of calcium thus forms an 
excellent salt water bath, of very great service in many chemical prepara- 
tions. 
The apparatus which I use is composed : 
1. Of an iron boiler, containing the muriate of lime. 
2. Of a flat bottomed silver basin, (one of copper will answer if well 
tinned,) into which the tannin is to be placed. This latter is to be placed 
in the muriate of lime, which is to be raised to the boiling temperature. 
But to obtain a temperature of 120°, C, without burning the product, and 
without accident to the operator, it is necessary to take some precautions 
which are readily foreseen. 
Having disposed the apparatus with suitable precautions, and having 
cautiously set it in operation, that portion of the ether which preserves the 
tannin in the state of a thick liquid will readily volatilise, and the inferior 
part of the mass touching the basin will be converted into brilliant, nearly 
white, very light scales, forming a mass of greater bulk than before. 
Meanwhile, the upper portion remains colored and transparent, because it 
