1863 The manufacture of liquors, wines, and cordials

MANUFACTURE OF SULPHURIC ACID.

190

and in three hours from the time of lighting, the con densation of the gases having in that interval been completed, the doors are thrown open for from fif- teen to twenty minutes, to admit fresh atmospheric air, and to allow time for the residuary nitrogen to Preparatory to the next burning, the ope- rations are repeated with fresh charges of the mix ture, every four hours, both night and day, until the water has attained the requisite acid- impregnation. When it is transferred to leaden boilers, and other- wise treated, as just explained, the quantity of the charge for each burning is determined by the size of the chamber, allowing one pound of the mixture for every three hundred cubic feet of atmospheric air which it may contain. As in the manufacture of sulphuric acid, the nitre is the most expensive material. Many plans have been resorted to for the purpose of obtaining the necessary nitrous acid at a cheaper rate. One plan has been to treat molasses, or starch, with common nitric acid. In this case the manufacturer obtains oxalic acid as a collateral product, which serves to diminish his expenses. In some manufactories of sulphuric acid nitrate of soda is substituted for nitre ; the advantages of the former salt are its greater cheapness, and the ci> escape.