316 



NATURE 



[June 19, 1919 



apposite examples, is shown in Fig. i. The sand 

 grade consists preferably of coarse or medium sand, 

 the Belgian material being therein more suitable than 

 that from Cornwall (St. Erth). Verticality of the 

 graph over the region of the sand grade marks the 



___fs K- 





Alunvna ^ ^__ ^ __ , 



10 0-5 0-25 01 



-^Grade-sizes (diameter i 



05 

 Millimetres) 



001 

 • Mechanical Composition, 



Fig. 2. — " Cornish rei " sand for stie! m )uldiiig : 

 composition with grade. The large 

 sample before elutriation. 



;raphical representation of variation of chemica 

 indicate the chemical composition of a "bulk' 



preponderance of this grade, and horizontality over 

 the region of the fine sand and silt grades indicates 

 the relatively subsidiary character of the latter. This 

 peculiarity in grading of moulding sands may be inter- 

 preted in the light of their behaviour in the foundry. 

 A maximum pore-space would be yielded by a rounded 

 sand uniform in grade. The 

 presence of coarse, rounded 

 grains in the sands mentioned 

 above, therefore, permits the 

 escape of the gases and vapours 

 produced when the hot metal 

 enters the mould. In short, the 

 mould is said to be well" vented." 

 If silt and fine sand were present 

 in any considerable quantity, this 

 natural venting would be gravely 

 impaired. The clay grade is re- 

 quired to act as the "bond" 

 uniting the sand grains together. 

 Both the Cornish and Belgian 

 sands mentioned have a strong 

 bond — that is, contain a rela- 

 tively high proportion of true 

 clayey material (14 to 20 per 

 cent.). The ideal condition in 

 which the clayey bond exercises 

 a maximum effect is that of a 

 pellicle, as thin as possible, com- 

 pletely enveloping each quartz 

 grain. 



In contradistinction to such 

 peculiarly graded sands (for they 

 are abnormal geologically, and 

 hence are of restricted occurrence) 



are the well-graded materials desirable for glass manu- 

 facture. A sand such as that from near King's Lynn 

 (Fig. i), which contains a high percentage of grains 

 belonging to the medium sand grade and practically 

 no silt or clay, passes freely and evenly into melt, 

 NO. 2590, VOL. 103] 



thereby assisting to produce a homogeneous glass as 

 rapidly as possible. 



The inter-relation of chemical and mechanical con- 

 stitution is well brought out in moulding sands of 

 good quality like these from St. Erth, Cornwall, and 

 Fontenay aux Roses, near Paris 

 (Figs. 2 and 3). Not only must the 

 sand be composed of suitable grades ; 

 it must ajso be highly refractory to 

 heat, and capable, for example, of 

 withstanding the effects of molten 

 steel run from converters and electric 

 furnaces. ("Open-hearth" steel is 

 not so exacting upon the sand.) The 

 refractoriness to heat is indicated by 

 the fact that chemical analysis of the 

 coarse, medium, or fine sand grades 

 shows them to be high silica sands 

 containing only small proportions of 

 alkalis and alkaline earths. 



The variation of chemical com- 

 position with grade is expressed 

 pjraphically in Figs. 2 and 3, where 

 the high silica content of the sand 

 grades is evident. Analysis of the 

 clay grade shows that its composition 

 closely resembles that of many first- 

 (lass British fireclays, which are also 

 very refractory. In addition, the 

 diagram illustrates the presence of 

 a relatively high percentage of 

 hvdrated ferric oxide ; this compound 

 •-"> is probably present in a colloidal 



form, and is responsible for much of 

 the wonderful strength of the bond of the moulding 

 sand. 



The widespread American practice, now of maliy 

 years' standing, of milling together a naturally oc- 

 curring siliceous sand with a good fireclay and 



'I 



\ 



certain amount of an artificial bond, such as dextrin. 



10 0-5 0-25 01 005 



-* Grade -sizes (diameter in Millimetres) • 



001 

 Mechanical Composition. 



3._" French red " sand for steel moulding: graphical representation of variation of chemical 

 composition with grade. The large crosses + indicate the chemical composition of a "' bulk ' 

 sample before elutriation. 



flour, molasses, etc., is in this connection verj 

 significant. It yields an indication of the manner in-j 

 which the absence of the remarkable naturally bondedj 

 sands of Western Europe has been compensated byj 

 the production of an artificial mixture of somewhat 



