138 CASEIN. 



treated in the same way can be used for stereotype matrices, 

 and will keep for any length of time, by reason of its light- 

 ness and durability. It is thus evident that the field of 

 application open to casein is practically illimitable. 



METACHROMOTYPE PAPER. 



This paper, which is used for transfer pictures, is pre- 

 ferably made of a fairly good, lightly sized (if at all) but 

 smooth paper, capable of readily absorbing the thin solution 

 of casein (preferably prepared with sodium bicarbonate) and 

 of softening with similar ease when it has to be released. 

 Since imperfectly coating the paper with the adhesive will 

 result in a defective impression, it is evident that the coating 

 must be perfectly uniform. The operation is best performed 

 with a flat brush, the paper being spread on a table and the 

 casein solution applied smoothly by working the brush in one 

 direction. If necessary the coating is repeated, the brash 

 being then worked at right angles to the previous direction. 



The prepared paper is next hung up to dry on lines in a 

 gently warmed room, preferably in a stretched condition to 

 prevent it curling. It is afterwards cut into sheets and 

 packed, either with or without calendering to smooth en the 

 surface. 



SIZING PAPER WITH CASEIN. 



Notwithstanding the most scrupulous care bestowed on 

 the preparation of the resin soap used in sizing paper, it has 

 been found impossible to impart the desired firmness and 

 impermeability to the paper by the use of vegetable size. In 

 view of the large quantities of casein now obtainable as a 

 result of buttermaking on the large scale, which casein has 

 had only a very limited application, it seemed advisable to test 

 its suitability for sizing paper ; and with this object compara- 

 tive experiments were carried out by Dr. Zanardi with resin 

 soap and casein solution. 



