THE PHYSICAL PROPERTIES OF CLAY. 95 



Explanation of table. — The clays tested were the following : 



648. Fat, black micaceous clay, of Clay Marl I from Maple Shade (Loc. 149). 



655. A clay marl. Exact locality unknown. 



663. A Pleistocene clay from Vineland (Loc. 183). 



665. A yellow, finely gritty, Cohansey clay, heavily stained with limonite 



from Toms River (Loc. 206). 



696. Black, Asbury clay from west of Asbury Park (Loc. 217). 



703. Sandy, Raritan clay from near Fish House (Loc. 136). 



717. A very plastic clay from Clay Marl III, south of Woodbury (Loc. 156). 



728. Hudson River shale from Port Murray (Loc. 282). 



The bricklets had been standing in a warm room for several 

 weeks and although they appeared perfectly dry, they were 

 placed in a hot-air bath and kept at a temperature of no° C. 

 for a day, being weighed both before and after. This drove off 

 the moisture remaining in the pores, and the resulting loss in 

 weight indicated in the third column of the above table shows 

 the quantity of moisture that may remain in a brick after the 

 air shrinkage has ceased. It is least in the sandy, lean clays, 

 and highest in the black one which is colored by organic matter. 

 The second column indicates the per cent, of air shrinkage, cal- 

 culated upon the length of a freshly molded bricklet. The fourth 

 column, headed 500 C. (932 F.), gives the loss in weight from 

 the thoroughly dried condition up te> 500° C, calculated on the 

 weight of the air-dried sample. The following columns give the 

 additional loss in weight for each ioo° C. (180 F.), as well 

 as the fire shrinkage taking place in this temperature interval. 

 From an inspection of the table it is seen that most of the 

 volatile substances, such as the chemically combined water con- 

 tained in kaolinite, mica, or limonite, and organic matter pass 

 off before 500° C. (932 F.), and that an additional appreciable 

 amount is expelled between 500 C. and 6oo° C. Between 

 600 ° C. (1112 F.) and 1100 C. (2012 F.) there was a 

 small but steady loss, while in one case (No. 663), there was 

 even a gain in weight at iooo C. (1832 F.). Two samples, 

 Nos. 696 and 665, showed a high loss at 500 C. and 6oo° C, 

 as compared with the others, but this was due to 1 the former 

 containing considerable organic matter, and the latter having a 



