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SCIENCE 



[N. S. Vol. XXV. No. 652 



kaolinization of feldspar is never due to 

 atmospheric action, but always to post-vol- 

 canic pneumatolytic and pneumato-hydato- 

 genic processes. 



The very fact that many of our kaolins pass 

 into undecomposed feldspar or feldspathic rock 

 when the limit of weathering is reached, shows the 

 incorrectness of such a broad statement (p. 7). 



The discussion of the origin of clays is fol- 

 lowed by a fairly complete description of the 

 secondary changes both mechanical and chem- 

 ical, in clay deposits, a feature often omitted 

 in similar works. 



In most treatises the statement is made that 

 kaolinite is the basis of all clays, which are 

 thus to be regarded as mixtures of kaolinite 

 with other minerals. The incorrectness of 

 this statement, the author thinks, will be 

 made evident by an examination of any series 

 of kaolin analyses, which will show that the 

 alumina-silica ratio is often higher than that 

 required for kaolinite, and this seems best ac- 

 counted for on the supposition that some of 

 the other clay-like minerals, such as pholerite 

 or halloysite, are present. The fact is also 

 pointed out that neither the chemical nor the 

 rational analysis can in every case be relied 

 upon to give certain information concerning 

 the mineral composition and other characters 

 of a clay. Thus, a washed kaolin might hav« 

 as much as twenty per cent, of white mica, 

 and yet on analysis show a composition ap- 

 proaching rather closely to that of kaolinite. 

 And, moreover, kaolinite, pholerite, halloysite, 

 and muscovite are all decomposed by hot sul- 

 phuric acid, and in a rational analysis would 

 be reported as clay substance. This is unfor- 

 tunate, since mica is not refractory and should 

 not, therefore, be grouped with the other three 

 (p. 167). 



In Chapter 11. the various minerals occur- 

 ring in clay and their influence on its be- 

 havior, especially as regards shrinkage en-i 

 fusibility, are quite fully treated. It has long 

 been known that titanic oxide is of imiversal 

 occurrence in clays, though seldom shown in 

 analyses. Experiments of the author re- 

 cently carried out with mixtures of kaolinite 

 and titanic oxide up to 5 per cent., prove that 



even small amounts of this substance lowei 

 the refractoriness of clays, one half per cent, 

 bringing the fusing point down half a cone. 

 The importance of determining the titanium 

 in a refractory clay is thus made clear. 



Of the physical properties of clays, plasticity 

 is in many respects the most important, and 

 perhaps the most difficult to explain. The 

 author considers the conception of plasticity 

 as expressed by many as too narrow. He 

 remarks : 



A broader conception, and probably a more satis- 

 factory one to the physicist, would be to defin* 

 plasticity as the property which many bodies po3 

 sess of changing form imder pressure, without 

 rupturing, which form they retain when the pres- 

 sure ceases, it being understood that the amount 

 of pressure required, and the degree of deforma 

 tion possible, will vary with the material (p. 94) 



This definition would include many bodies 

 besides clay, which are excluded by the nar 

 rower definitions. 



The various theories put forward to explain 

 the cause of plasticity are passed in review, 

 with the conclusion that plasticity is not de- 

 pendent upon any single cause advocated by 

 these theories, but by a combination of them. 

 The relations of texture to tensile strength 

 are illustrated by experiments of Orton, Beyer 

 and Williams, and the author, which go to 

 show that in those clays having the highest 

 tensile strength, the percentages of fine, me- 

 dium, and coarse particles are nearly equal, 

 and that an excess of either coarse or fine 

 grains lowers the tensile strength. 



In Chapter IV. the various kinds of clays, 

 in the order of the purposes for which they are 

 used, and beginning with the highest grades, 

 are described as to their chemical and phys- 

 ical properties. These characters are further 

 illustrated by typical physical tests and 

 chemical analyses. The latter part of this 

 chapter, devoted to descriptions of methods of 

 mining and manufacture, might by some be 

 criticized for lack of sufficient detail, but the 

 book is not intended to be a treatise on the 

 manufacture of clay products alone, and too 

 much technological detail would be clearly out 

 of place. 



The illustrations are well selected, not for 



