108 CHEMICAL AND PHARMACEUTIC MANIPULATIONS. 
burner, Fig. 6, over the jet 3, Fig. 5, and to depress it so 
Fg. 7. 
00 
much that its orifice may extend a short way into the flame 
for heating a vessel of small surface, and still further for 
vessels of greater superficies. The gas being turned on and 
inflamed, the treadle is then worked with the foot, slowly 
at first, until the current of air thus forced up through the 
tube changes the white and quiet flame into one of a pale 
reddish tint and ragged outline. If too much air be driven 
through, the flame becomes bluish, and the heat becomes 
less intense. 
Desiccation of Solids. 
"Those saline matters which readily yield all their watei 
by exposure may be reduced to powder or effloresced by 
subjecting them in thin layers to a draught of dry air which, 
if necessary, may be moderately heated. For this purpose 
as well as for that of drying crystals which do not effloresce, 
it is necessary in manufacturing laboratories to have a 
special apartment. This room should be smoothly plastered 
within, and need not be of large size. As a means of ven- 
tilation its opposite sides are pierced with small holes, 
which, to prevent the admission of dirt, are covered with 
