REVIEWS 



The Foundry Sands of Minnesota. By G. N. Knapp. Bull. i8, 

 Minn. Geol. Survey, 1923, pp. 105. figs. 13, tables 17, 



Foundry sand has been defined heretofore as a sand or loam which 

 has the following properties: it must contain sufficient clay or other 

 binding material to enable it to stand up in the mold; it must be suffi- 

 ciently porous to allow steam and gases to escape, and must be siifficiently 

 refractory to resist fusion. But precise measurement of any of these 

 properties has rarely been attempted, and figures expressing these proper- 

 ties quantitatively are very meager, or wanting. 



The purpose of the investigations described in this Bulletin was to 

 place these properties on a quantitative basis. A careful measurement 

 of each of the essential properties of molding sands was undertaken, and 

 the absolute and relative values of the results are given in definite figures 

 and percentages. 



The clay content of various types of foundry sands was accurately 

 determined by elutriation, and is given in percentages by weight. The 

 bonding power of the elutriated clay was found to vary with the kind of 

 clay, and this difference in bonding power was attributed to the probable 

 variation in the amount of colloidal material present in clays of different 

 types. The colloidal content was not determined. 



The moisture content of sands in actual foundry practice was 

 found to vary from 1.7 per cent to 12 per cent by weight, this variation 

 being due to proportioning of the fine and coarser sizes in the sand, the 

 clay content, and the kind of clay. The amount of colloidal material 

 was probably also an important factor. 



The mechanical analyses of the sands and loams were carried to a 

 greater degree of refinement than heretofore. The laboratory work 

 demonstrates that sizing of sands by screen sieves cannot be done accur- 

 ately with the clay and silts present, because of the inevitable presence 

 of clusters of fine grains, and the adhering of fine grains to the coarse 

 ones. The silts are shown to play an important role in granulation, on 

 which permeability in molded sands largely depends. 



The permeability of the sands in the natural condition, as well as 

 in the molded state, was determined by actual measurement which had 



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