r94 NEW YORK STATE MUSEUM 



posits, and sand from solid sandstone. As the first two contain 

 clay, they are carefully heated to dehydrate the clay. The sand- 

 stone is crushed under a hammer, and mixed with an equal 

 weight of each of the other two kinds of sand. The mixture 

 is ground by iron balls in a revolving drum, and afterward 

 passed through a flannel-lined cylinder, which moves up and 

 down; it is thus obtained in the state of the finest flour, which 

 in molding may be made to receive the most delicate impres- 

 sions." Analyzed by J. Spiller 



12 Employed in Japan. Analyzed by W. J. Ward 



Porosity. The pore spaces between the grains of sand must 

 be large enough, and numerous enough, to permit the free pass- 

 age of air, and of such gases as may be formed during the oper- 

 ation of casting. At the same time, the pores should not be 

 so large as to permit any of the molteu metal to enter the sand. 



The porosity of a sand will depend largely on the size of its 

 constituent grains, and on the relative proportions of the var- 

 ious sizes. Porosity will also be dependent on the amount and 

 character of the material which gives the sand its bond. A 

 molding sand whose bond, in the natural state, is dependent 

 partly on the presence of organic matter will become more 

 porous on firing; while a sand held together by clayey material 

 will tend to become less porous at high temperature, owing to 

 the baking of the clay. 



Fineness. The fineness necessary in the sand depends largely 

 on the character of the work for which it is to be used. Mold- 

 ing sands are roughly graded at the point of production, but 

 most foundries require much more careful grading than this. 

 Certain plants issue regular specifications to cover this point, 

 and buy only such sands as have been graded for fineness to 

 meet such specification. 



Tenacity. The tenacity, or " bond," of a sand is an important 

 quality, as on it depends the capacity of the sand, both to take 

 the shape of the pattern properly, and to retain this shape 

 despite the weight of the metal poured into it. The bond of a 

 sand is usually due to the presence either of organic matter, 

 or of clay. Organic matter, while an excellent bond for an 



