THE NONMETALLIC MINERALS. 



475 



quoted by Crookes and Rohrig, 1 the "quality of the sand for molding 

 depends less on its chemical composition than on its physical proper- 

 ties, namely, whether the grains are round, angular, scaly, etc., and 

 whether they are of uniform size. The adhesiveness is dependent 

 not alone on the quantity of clay, but upon the angularity of the 

 grains, and by a mixture of smaller and larger grains. Reinhardt states 

 that to the naked eye, a good sand should consist of particles seem- 

 ingly uniform in size, with a sharp feel to the touch. When strewn 

 upon dark paper it should show no dust, and when moistened with 

 from 10 to 20 per cent of water it must be capable of being formed 

 into balls without becoming pulpy or being too easily crushed. 



Of the above No. I is from Charlottenburg, Germany; No. II, a sand 

 employed for bronze castings in Paris foundries; No. Ill, sand from 

 Manchester, England; No. IV, from near Strom berg; No. V, from Ilsen- 

 burg, in the Hartz Mountains; No. VI, from Sheffield, England; No. 

 VII, from Birmingham, England, and No. VIII. from Liineburg. 



The sand from Ilsenburg, the composition of which is given in column 

 5, is stated 2 to be prepared by mixing "common argillaceous sand, 

 sand found in alluvial deposits, and sand from solid sandstone." In 

 preparation the first two are carefully heated to dehydrate the clay 

 and then mixed, equal proportions of each with the same amount of 

 sandstone. The mixture is then ground and bolted, the product being 

 as fine as flour and capable of receiving the most delicate impressions. 



According to D. H. Truesdale, 3 the four essential qualities in mold- 

 ing sand are, in the order of their importance, (1) refractoriness, (2) 

 porosity, (3) fineness, and (4) bond. These qualities are dependent 

 mainly upon the varying properties of siliceous sand and clay, the 

 refractory nature being governed by the absence of such fluxing con- 

 stituents as calcium carbonate, the alkalies, or of iron oxides. Since 

 in nature it is not always possible to obtain the admixture of just the 

 right proportion, artificial mixtures are often resorted to, as mentioned 



1 A Practical Treatise on Metallurgy, II, p. 626. 



2 Percy's Metallurgy, 1861, p. 239. 



3 The Iron Trade Review, October, 1897, p. 24. 



