; try-cocks at different hights for examination of contents; discharge-cocks at different hights for drawing off the liquid oil and the water; discharge-hole, with cover at the bottom, to remove the solid matter from the bones and fibrine.
In Everett's apparatus (Fig. 2812) the digester, containing the fat, is surrounded by an outer shell constituting a hot-water and steam space, to which it is connected by stay-rods, which unite the waterspace at bottom with the steam-space at top, and passapparatus consists of an exterior casing of masonry in which the digester, which may be of the form shown either in the upper or lower figure, is placed.
In the first it is stationary, and consists of an inner and outer shell, between which
Everett's lard-rendering tank. and through flues in the inner one A A the heat circulates.
The rendered fat, in a fluid condition, descends from shelf to shelf, and is strained through the perforated bottom C, whence it is drawn off. The furnace has an
acid, and converted to oxide, and finally to metallic tin.
d. Alexander Parkes, in the same year, employed mercury, forming a tin amalgam, which was subsequently retorted.
The use of mercury is prejudicial to health.
e. The same person, in 1858, recommended concentrated oil of vitriol.
f. J. M. Patterson, of New Jersey, patented, in 1863, the use of a bath of melted lead, to form an alloy with the tin, which, suitable proportions of tin being added, may be used as solder.
g. Mr. Everett, of New York, in 1865, proposed to use tinscraps in smelting galena.
h. Sturdevant and Harmon, New York, propose to melt off the tin from the scraps by means of hot air and steam in a cylindrical retort with a perforated, inverted conical bottom.
i. Ott's method consists in the solution of the tin and lead of the scraps in muriatic, with a slight admixture of nitric acid, the precipitation of the lead from this solution by means of sulphuric acid, and the final precipitation of the