40 IOWA ACADEMY OP SCIENCES. 



of the copper or by Traube's theory which is backed up by 

 .almost convincing evidenced 



Stannous chloride will reduce sulphuric acid with formation 

 of hydrogen sulphide and free sulphur, an analogous reaction 

 in which the assumption of "nascent" hydrogen is inadmissible. 



SMoritz Traube, loc. cit. and Bet:, 18, 1877, etc. 



CLAYS OF THE INDIANOLA BRICK, TILE AND POT- 

 TERY WORKS 



L. A. YOUTZ, INDIANOLA. 



Analyses of several clays from a brickyard at Indianola have 

 recently been made by me to go into a report of the Geological 

 Survey of Warren county. Though it has been said that a 

 knowledge of the constituents of a clay, determined by a purely 

 chemical analysis, is of very little value to a practical brick- 

 maker, yet in comparing the analyses of these clays and those 

 from other vicinities, it seems that points of great value to the 

 manufacturer are made plain, and points that can be derived 

 from no other source. So I wish to give a few ideas which 

 came to me as I made the comparison, as points, of local inter- 

 est at least, were, it seems to me, clearly brought out. 



In order to get an intelligent idea of the value of this clay 

 for brick and tile it may be helpful to give a short outline of 

 some of the qualities of clay for the various kinds of brick. 

 The quality and character of brick depends, of course, pri- 

 marily upon the kinds of earth used; the mechanical mixing, 

 drying and burning being important items, however. 



The varieties of clay most frequently used for common 

 bricks are three. The so-called blue clays, hydrated aluminum 

 silicates, combined with small quantities of iron, calcium, mag- 

 nesium and alkalis; sandy clays or loams, and marls which con- 

 tain a large proportion of lime and magnesium. In addition to 

 these are the clays for special kinds of brick, as fire-brick, 

 pottery, terra cotta, etc. Hydrated silicate of aluminum is 

 infusible even at the most intense furnace heat, but if these be 

 mixed with alkalis, or alkali earths, it becomes fusible, and in 



