852 NEW YOEK STATE MUSEUM 



Filling paper 



Clay is one of tlie several substances used for tMs purpose. 

 It is mixed in with the paper pulp during the process of manufac- 

 ture, the object of this being that the fibers of the pulp shall enmesh 

 a certain amount of the clay particles which are in suspension in 

 the water in which the pulp is. The plasticity and sandiness of the 

 clay no doubt exert some influence on the degTee of successof the 

 operation, for it is found that a. given paper will often retain a much 

 greater proportion -of some clays than others, those of which the 

 greatest quantity is retained being the most plastic, of the several 

 tried. Sand is an undesirable constituent of paper clay for the rea- 

 son that the sand grains tend to wear out the wires of the screens 

 through which the materials have to pass. In certain lines at least 

 clay is not used as much for filling as it formerly was. The color 

 of the clay in its raw condition is all important for the' higher 

 grades of paper. For the best quality a very fine white kaolin or 

 sedimentary clay is used, it being first carefully washed, but for 

 the commoner grades, specially the colored ones, the manufacturer 

 does not as a rule have to search very far in order tO' find the right 

 material, as the requirements are not so strict. 



Food adulterants 



This use of clay is self-evident. It is used as an. adulterant of 

 those food products which it resembles in color, and which are used 

 either in a powdered condition or caked form, either of which 

 would tend to hide the presence of the adulterant. 



Ultramarine manufacture 

 Kaolin in its washed condition or even very fine-grained, white 

 sedimentary clays are used in the manufacture of ultramarine to 

 serve as a nucleus for the coloring material to gather round. For 

 this work the clay should be as low in iron and lime as possible, 

 and an excess of silica is undesirable, but if too little is present it 

 may be added in the form of finely powdered quartz. 



Polishing and abrasive materials 



Many clays exert a combined polishing and abrasive action on 

 account of the very finely divided grains of sand which they con- 

 tain. The well-known Bath brick which has such an extensive 



