MISCELLANEOUS CLAYS. 199 



The fineness of grain is probably accountable for the 

 low tensile strength and comparatively low temperature 

 of vitrification and fusion. As far as the composition is 

 concerned it is not unlike some of the potters clays used 

 it the United States, but its low tensile strength would 

 probably act against its utility for this purpose, unless 

 mixed with a more plastic clay. For building materials 

 it would no doubt work all right. Being of fine uniform 

 grain permits the production of a very smooth surface on 

 the ware. 



(No. X. S.) 



CLAY FROM W. J. BECKWITH'S. 







COLBERT CO. 



A moderately fine-grained, homogeneous, brittle, porous 

 clay, with a semi-couchoidal fracture. In water it slakes 

 slowly to particles mostly under one-sixteenth inch in size. 



When mixed with 28 per. cent, of water it gave a lean 

 mass of somewhat gritty feel, which shrunk 5 per cent, 

 in drying and 6 per cent, in burning, or a total shrink- 

 age of 11 per cent. The clay had to be dried and burned 

 slowly to prevent cracking. 



Air dried briquettes made of the mud had an average 

 tensile strength of 22 Ibs. per square inch, and a maxi- 

 mum strength of 38 Ibs. 



Incipient fusion occurs at 2050 F., vitrification at 

 2250 F., and viscosity at 2450 F. 



The clay burns to a deep buff body, and requires care- 

 ful heating to avoid cracking. 



An analysis of the material gave the following results: 



