MAGNESIA BRICKS AND OXYCHLORIDE CEMENTS. 163 



made from magnesium chloride (see p. 158) the magnesia is free from 

 carbon dioxide, and though it sets and hardens less rapidly, no cracks 

 appear. 



The commercial magnesium chloride used in the preparation of 

 Sorel stone, etc., usually contains sulphuric acid. As this acid and 

 its compounds spoil the appearance and the durability of the stone 

 produced, it is eliminated from the magnesium chloride by treatment 

 with barium hydrate or barium carbonate. In practice,* the magnesium 

 chloride is dissolved in water to form a solution of 20 to 25 Baume, 

 and the barium hydrate or carbonate is added by degrees and carefully 

 stirred until the precipitate of barium sulphate ceases to increase. The 

 amount of reagent required is usually between 6 and 10 per cent of 

 the weight of the magnesium chloride treated. 



Magnesia cement is used very extensively f as a binder, in connection 

 with briquetting, in the manufacture of artificial building-stones, tiles, 

 grindstones, and emery- and polishing-wheels. Its binding quality is 

 very considerable, and it is very plastic and cheap. A good mixture 

 for this use consists of 25 parts of magnesium chloride (45 per cent 

 solution), 25 parts magnesia (93 per cent MgO), and 50 parts water. 

 About 5 Ibs. of this mixture will serve to cement 95 parts of stone, 

 emery, etc. The resulting blocks are very solid and harden thoroughly 

 within a few hours. 



Gillmore, in 1871, prepared a report on certain American patented 

 products based upon Sorel cements. As this report is still the only 

 complete discussion of the subject it is reprinted below, almost verbatim. 



"The several steps in the process, beginning with the raw magne- 

 site, are briefly as follows, viz. : 



"First. The magnesite is burnt in ordinary lime-kilns, at a dark 

 cherry-red heat, for about twenty-four hours. The result is protoxide 

 of magnesium, which is next ground to fine powder between horizontal 

 millstones, furnishing what the Union Stone Company style 'Union 

 cement'. 



"Magnesite has been procured from various localities. That from 

 Greece, California, Maryland, and Pennsylvania contains about 95 

 per cent of carbonate of magnesia, the residue being mostly insoluble 

 silicious matter. The burnt product is perfectly white. A magnesite 

 is procured in Canada which contains from 60 to 85 per cent of car- 



* Journ. Soc. Chem. Industry, vol. 21, p. 257. 1902. 



f Schorr, R. The briquetting of minerals. Eng. and Mining Journal, vol. 74, 

 p. 673. 1902. 



