209 



Brunswick, generally of much greater purity than the American or 

 German earth, and it is also found to some extent in the province of 

 Quebec. 



It is extensively used for the manufacture of water-glass or soluble 

 silica, and for the coverings of boilers and steam pipes for which purposes, 

 owing to its great non-conductive properties, it is especially adapted. 

 As a polishing powder it is also extensively employed, and for some 

 years was an ingredient in the manufacture of dynamite, as an absor- 

 bent of the nitro-glycerine which enters into the manufacture of this 

 explosive. For this purpose, however, wood-pulp has now to a large extent 

 superseded it. In the lining of safes and for the protection of exposed 

 portions of buildings, it is also largely used, but it can never compete 

 with asbestus fibre in the peculiar processes to which that product is 

 now applied. 



Another n^n-conducting material which enters largely into compe 

 tition, both with asbestus and infusorial earth, is the substance known 

 as mineral wool,. This is an entirely artificial preparation, and its 

 discovery whs doubtless due to the fact that a somewhat similar 

 substance occurs in a state of nature in connection with certain volcanic 

 eruptions, more especially in those of the Sandwich Islands, where the 

 slaggy volcanic licpietied matter is acted upon by blasts of air and blown 

 out into long silky fibres, which have received the name of " Pele's 

 Hair." Mineral wool, or slag wool, is formed artificially in a somewhat 

 similar way, viz., by subjecting a stream of molten slag from a blast 

 furnace to a jet of steam or compressed air, by which means the slag is- 

 broken up into minute particles, generally with a small fibrous end or 

 tail, which accumulate as the)' fall and resemble masses of roughly 

 teased out cotton. The solid particles which form the head of ea<"h 

 minute atom are subsequently detached and the finer fibres carried over 

 into a separate chamber, when they are ready for use. This material 

 possesses wonderful properties as a non-conductor of heat or sound, lias 

 great lightness, and is absolutely fireproof. It is extensively employed 

 as a material for covering boilers, steam-pipes, and for lining buildings 

 to render them tire, sound and vermin proof. While, therefore, it 

 competes very successfully in many points with asbestus as a non- 

 conducting substance, like infusorial earth it has not the property 



LIBRARY] 30 



