THE MANUFACTURE OE CALOMEL IN JAPAN. 5 



the earth is seen to consist largely of colourless quartz grains. Besides 

 the quartz a very little biotite is seen sparkling through it. The fresh 

 damp earth does not form a compact mass, but u slightly cohering 

 aggregate of damp crumbs. This texture aj)pears to be due to the 

 earth being a mass of quartz in small grains from the size of a hemp 

 seed down to that of impalpable particles, held together by plastic 

 clay. For use that which does not contain coarse quartz grains too 

 abundantly is selected, and is made into briquettes and moderately 

 baked on the hearth of tlie tire-place under the calomel pots. These 

 briquettes are then as light and porous as the ])repared porous clay 

 used in Fletcher's gas-furnaces. The raw earth air-dried is readily 

 rubbed into its constituents by the fingers ; and the baked briquettes 

 very easily and ra])idly reduce to a soft powder, quartz grains and all, 

 in the ai^ate mortar. I'lie larger grains of quartz in the raw earth are 

 also verv brittle. I ha\e treated thus fullv of the mechanical charac- 

 ters of tlie earth, because probably nuidi of its efficiency is due to 

 them. l:>ut its chemical character also calls for notice. As baked 

 ready for use it contains in the thoroughly air-dry condition still ô 

 per cent, and mui'e of water. Before ignition it is almost entirely 

 decomposed l)y sulphuric acid, either in some days in the cold or 

 quickly by heat. It is also largely acted u})on by hot hydrochloric 

 acid, and heated in sealed tubes with this acid to 11^0-150,° it is almost 

 as fully de('om])oscd as Ijy sul|)liuric acid. It contains practically no 

 silica soluble in hot sodium-carbonate solution, ])ut after acid 

 treatment yields, of course, uiuch silica to this reagent. The com- 

 position of the eai-th, as found in use at the works, but rendered 

 anhydrous is as follows : — 



