156 CEMENTS, LIMES, AND PLASTERS. 



into liquid form. For every ton of magnesite about 500 Ibs. of coke 

 is burned, and this, containing about 97 per cent of carbon, also fur- 

 nishes considerable gas. The steel cylinders for holding the liquid 

 gas are ^ inch thick and 5 by 49 inches long, and hold about 25 Ibs. 

 The pressure on the cylinder at 60 F. is about 850 Ibs., a three-stage 

 compressor being used. In shipping the liquid gas through the central 

 valleys and to Arizona the heat in the cars sometimes runs as high as 

 145, the pressure being increased thereby. The cylinders containing 

 the liquefied gas are shipped to soda-water manufacturers, ice-fac- 

 tories, refrigerating-plants, breweries, bar-rooms, etc. The cylinders 

 with the liquid gas are shipped all over the Pacific coast from San Fran- 

 cisco, even the British war vessels stationed at British Columbia using 

 the gas for their refrigerating-plants. The San Francisco carbonic- 

 acid-gas makers use about 1000 tons of crude magnesite annually. 



As stated, the wood-pulp paper-mills of California and Oregon use 

 the calcined magnesite. They transform it into a sulphite of magnesia 

 and -use it as a digester for the wood pulp. To make this sulphite they 

 put the material into a tank and pass sulphurous fumes through it. 

 After being used as a digester they add a little lime and make the ' pearl 

 hardening ; of commerce to be used as a ' filler ' for the paper. " 



Magnesian Limestones as Sources of Magnesia. 



Highly magnesian limestones, approaching dolomite in composition, 

 may be regarded as possible sources of magnesia. The general char- 

 acters of such limestones are discussed in some detail in earlier chapters 

 of this volume, and reference should be made to pp. 90-91 for data 

 on these points. 



Occurrence of magnesian limestones in the U. S. Magnesian lime- 

 stones are so widely distributed throughout the United States that 

 no satisfactory summary of their distribution can be given here. On 

 pp. 92-94 is given a list of reports on the limestones of the various 

 states and territories. Reference to these reports will furnish data 

 on the local distribution and composition of magnesian limestones, as 

 well as of other types. 



Analyses of magnesian limestones. In the following table analyses 

 of a number of highly magnesian limestones from various localities 

 in the United States are presented. It will be seen that these range 

 from 15 to over 22 per cent in magnesia (MgO), which is about 

 equivalent to a range of from 32 to 45 per cent magnesium carbonate 

 (MgC0 3 ). 



