MAGNESIA BRICKS AND OXYCHLORIDE CEMENTS. 165 



tained by crushing and grinding, that it is difficult, without the appli- 

 cation of chemical tests, to detect any difference in either texture, 

 color, or general lithological appearance. 



"Strength. In strength and hardness this stone greatly surpasses 

 all other known artificial stones, and is equaled by few, if any, of the 

 natural stones that are adapted to building purposes. The artificial 

 marble takes a high degree of polish, being in this respect fully equal to 

 the best Italian varieties. 



"Some trials of 2-inch cubes at the Boston Navy-yard gave the 

 following results, reduced to the crushing pressure upon one square inch: 



No. 1, crushing strength per square inch 7,187 Ibs. 



No. 2, " " 11,562^ " 



No. 3, " " 21,5624 " 



No. 4, " " " " 7,343i " 



" In none of these samples did the proportion of the oxide of mag- 

 nesium exceed 15 per cent by weight of the inert material cemented 

 together. This statement is derived from the treasurer of the company. 



" The principal business of the Union Stone Company up to the present 

 time has been the manufacture of emery-wheels. The great tensile 

 strength of the material may be inferred from the fact that in the proof 

 trials the wheels are made to revolve with a velocity of from 2 to 3 miles 

 per minute at the circumference. They do not usually begin to break 

 until a velocity of from 4 to 5 miles per minute is attained. 



"From a number of specimens of this stone furnished the writer 

 by the treasurer of the company, who also gave their age and com- 

 position as reported below, comprising coarse and fine sandstone of 

 various shades of color, hones, white and variegated marble, emery- 

 wheels, billiard-balls, concrete building-blocks, etc., some small blocks 

 were prepared and subjected to crushing with the results given in 

 Table 68. 



"Durability. The proofs of the durability of the Union stone rests 

 upon other evidence than that furnished by severe and prolonged climatic 

 exposure. In Boston, however, building-blocks have resisted two winters, 

 and at the present time appear to be, and doubtless are, harder and 

 stronger than before they were touched with frost. 



"Dr. C. T. Jackson, State Assayer of Massachusetts, reports upon 

 it as follows: 



" 'I find that the frost test (saturated solution of sulphate of soda) 

 has not the power of disintegrating it in the least. The trial was made 

 by daily immersions of the stone in the sulphate-of-soda solution for a 

 week and allowing the solution to penetrate the stone as much as pos- 



