404 ANNUAL BECOBD OF SCIENXE AND INDUSTRY. 



lcnitic mortar by the colonel is made by mixing a small 

 portion of sulphate of lime or sulphuric acid with the water 

 used, to which the lime is added, and the mixture ground to 

 a thin paste in a mortar-mill. After having been ground four 

 minutes, the remaining ingredients, which may be sand or 

 burned clay, are introduced, and the whole ground together 

 for ten minutes more. The sulphate of lime may be in the 

 form of plaster of Paris (gypsum), or sulphuric acid alone 

 may be employed. The best results, however, are obtained 

 with the acid, and Colonel Scott therefore uses it in prefer- 

 ence to the other substance, although this will answer effect- 

 ually for all ordinary purposes. The secret of the extraordi- 

 nary results obtained with this mortar lies simply in the fact 

 that the acid prevents the lime from slacking, and thus ena- 

 bles it to take in twice as much sand as when slacked, its 

 fieriness being controlled or brought into subjection. By 

 Colonel Scott's process any lime can be made selenitic, and 

 the more hydraulic it is the better are the results it gives. 

 The great value of this invention consists not only in the ex- 

 traordinary tenacity of the mortar thus obtained, but in its 

 great resistance to pressure. Thus it is stated that a block 

 of ordinary mortar, composed of one part of lime and two^)f 

 sand, with a breaking area of two and a quarter square inches, 

 usually breaks at seventy pounds' strain after being kept six 

 months. With Colonel Scott's mortar, however, a block of 

 the same dimensions, made of one part of Portland cement 

 and four parts of sand, and kept for one hundred and sixty- 

 seven days, required a strain of two hundred and six pounds 

 for breakage. Again, mortar one hundred and sixty-six days 

 old, made of one part gray lime, rendered selenitic, and three 

 of sand, required two hundred and forty-five pounds for 

 breakage, and another sample sustained a breaking force of 

 two hundred and fifty-five pounds. This mortar has been 

 applied with great advantage for imbedding tiles, which, as 

 is well known, frequently break loose in consequence of their 

 want of adhesion to the cement. In one experiment with the 

 selenitic cement the joint was broken only after a pressure of 

 one hundred and fifty-eight pounds, while with ordinary Port- 

 land cement fifty-eight pounds were sufficient to produce the 

 separation. 



The Mechanics' Magazine regards this as one of the c^reat- 



