K. MECHANICS AND ENGINEERING. 421 



and we must therefore conclude that, under certain circum- 

 stances at present not understood, gun-cotton is really ex- 

 plosive by simple ignition, and, as such, is to be handled with 

 the utmost precaution. 3 A, August 19, 1871, 134. 



CHARACTER OF SCOTT'S SELENITIC MORTAR. 



We lately gave an account of the new selenitic mortar in- 

 vented by Colonel Scott, of London, said to possess very great 

 merit, and to have been introduced into use on a very large 

 scale. A late paper by Schott upon this mortar discusses it 

 in a very comprehensive manner ; and, after an investigation 

 of the proper proportion and the qualities of the material, he 

 conies to the conclusion that a much greater range of pro- 

 portions, and a much larger number of ingredients than those 

 mentioned by the discoverer, will answer an equally good 

 purpose, thereby making it quite feasible to prepare it where 

 the substances first considered as essential are not to be found. 

 14 6 T ,CCII.,52. 



DINAS STONE, A NEW FIRE-PROOF MATERIAL. 



In the experiences of the Chicago fire (and in other simi- 

 lar calamities) as to the insufficiency of ordinary fire-proofing 

 materials, it may be well to call to mind the peculiar proper- 

 ties of a new artificial infusible stone lately invented in En- 

 gland, where it is known as Dinas stone, Flintshire stone, or 

 quartz brick. Its applications have been more especially in 

 the construction of steel furnaces, smelting furnaces, etc. ; but 

 it would seem particularly adapted, in consequence of its ex- 

 treme infusibility, to the preparation of absolutely fire-proof 

 safes and vaults. The Dinas stone proper is prepared from a 

 sandstone found in the Neath Valley of Southern Wales, oc- 

 curring partly as a rock and partly as a sand. The rock is 

 of a light gray color, with transparent edges, having the frac- 

 ture of crystallized quartz, and is prepared by crushing be- 

 tween cast-iron rollers to a coarse powder (with the excep- 

 tion of certain portions which are too hard to be thus treat- 

 ed), and then adding one part of lime and a suitable quantity 

 of water, and introducing the mass into iron moulds, where 

 it is pressed, by means of a stamp, upon an iron bed. After 

 the stones have been dried by artificial heat, while still upon 

 the iron bed, they are baked for seven days at an intense heat 



