142 CASEIN. 



pressed, dried in the air, and impregnated with a 1 per cent, 

 solution of zinc chloride. It is then redried, passed through 

 a'-j- to 1 per cent, aqueous solution of resin soap (prepared by 

 dissolving the resin soap in spirit and then in water), and 

 finally dried again in the air. The appearance is improved 

 by calendering. The finished article is elastic and com- 

 pletely fire- and water-proof. 



Asbestos millboard is prepared as follows : 

 Whereas long staple asbestos is required for spun articles, 

 the short fibres of ordinary quality are more suitable for 

 the purpose now in view. The short fibres separated from 

 those of longer staple by screening, prior to the spinning 

 process, are also used. The crude asbestos is put through 

 an opener to break up the fibres, and the material is then 

 softened with boiling water, after which it is ground in a 

 mill of exactly similar type to those employed in paper- 

 making. This consists of a long, rectangular, wooden, stone 

 or iron trough, filled with water and containing a revolving 

 roller provided with steel rails, underneath which is arranged 

 a massive oaken block inlaid with a row of knives. The 

 trough is divided into two parts by a central partition, over 

 which the asbestos fibres are flushed by the water into the 

 working compartment, where they are acted on by the roller 

 and knives. A hood placed above the roller prevents any of 

 the fibres being thrown out of the trough by centrifugal 

 force. Means are provided for setting the roller progressively 

 closer to the knives, so as to reduce the fibres more and 

 more. At the same time the medium casein, starch, gum, 

 etc. employed to bind the asbestos together, is usually 

 added in the mill. 



The further treatment of the asbestos pulp is 011 precisely 

 the same lines as in dealing with paper pulp for the manu- 

 facture of machine-made paper. The pulp is delivered on to 

 an endless sieve of metallic gauze, which receives a vibratory 



