L. MECHANICS AND ENGINEERING. 487 



projectile over 1700 pounds. Its range under these condi- 

 tions is estimated to be about six miles, and the force of the 

 projectile is such that it will pierce a plate of iron 25 inches 

 thick at a distance of one mile. The entire equipment of 

 the Inflexible comprises four pieces of ordnance of this same 

 size. 13 B, III., 100. 



CEMENT FOR MARBLE AND ALABASTER. 



We find in the Bulletin of the Chemical Society of Paris 

 the following; formula for a cement for marble and alabaster : 

 12 parts of Portland cement, 6 parts slaked lime, 6 parts fine 

 sand, and 1 part of infusorial earth are made into a thick 

 paste with silicate of soda or soluble glass. The object to 

 be cemented does not require to be heated. It sets in twen- 

 ty-four hours, and the fracture can not be readily found. 

 1 A, April 23, 185. 



PREVENTING INCRUSTATION IN STEAM-BOILERS. 



Among the many devices for preventing incrustation in 

 steam-boilers, that of lining them with thin copper plates is 

 said to be very effective. In certain cases, where the boiler 

 had strips of copper placed inside of it, other portions not 

 being covered, after a certain time it was found that the 

 uncoated portions were incrusted five and six times as much 

 as the copper- lined, the copper remaining also uncorroded. 

 It is claimed that in addition to the diminished amount of 

 incrustation and the less corrosion of the copper, the vapor- 

 ization is more complete, and that there is a corresponding 

 savin 2* of fuel. 



In the construction of a boiler to be lined with copper, it is 

 stated, and not without reason, that the weight of the boiler 

 is considerably reduced, since the iron plates may be of less 

 thickness, and the expense thereby diminished. It is remark- 

 ed, however, that the question still remains as to the galvan- 

 ic effect of the contact of the two metals, and the action of 

 waters less calcareous but more acid than that with which the 

 experiments referred to were prosecuted. 3 A, June 5, 715. 



COPPER' LINING FOR STEAM-BOILERS. 



The editor of the Engineering and Jfining Journal, in re- 

 ferring to the above suggestion of using a lining of copper 



