KAOLIN IN WISCONSIN. 27 



quartz. The bricks are reported as of extraordinary refractoriness, 

 and are even compared witli the famous Dinas silica bricks. 



Practical suggestions as to the use of the Wisconsin IxioJin to 

 make fire-h rick. — There appears to be every reason why a kaolin 

 brick, if properh^ made, should be of unusual value. A few sug- 

 gestions are given here as to its manufacture. First, then, the clay 

 must be selected in the pit, the red and bluish portions being re- 

 jected. The pure white are the best kinds, whilst some of the yel- 

 lowish kinds are much better than they appear at first sight. After 

 selecting, the kaolin should always be washed, to free it from fels- 

 pathic particles, which contain a large amount of fluxing alkalies. 

 The raw clay will never prove uniform in its capacity of withstand- 

 ing heat. This is what theory would teach, and, as I am informed 

 by Mr. J. J. Hagerman, of the Milwaukee Iron Works, is found in 

 practice to be the chief obstacle in the way of using the Wiscon- 

 sin clay. The fine clay obtained by washing should next be mixed 

 with a large excess of tolerably coarse angular quartz, for which 

 might be substituted in part, fragments of fire-brick. The mass 

 should now be moulded or baked carefully. In this way I am per- 

 suaded that an unusually good quality of biick might be prepared. 

 It will not do to make brick from this clay as the ordinary fire- 

 brick are made, on account of its extraordinary shrinkage on heat- 

 ing. Prepared in the manner I have suggested the kaolin brick 

 would far excel- ordinary'- fire-brick for all purposes, save where 

 contact vv^ith a highly basic slag is necessary, when it would be 

 inapplicable on account of its high content of free silica. I might 

 say in this connection that a number of places exist in Wisconsin 

 where the quartz for mixing with the kaolin might be obtained. 

 I am informed that since my examination of the Grand Rapids lo- 

 calities, a number of fire-brick have been mad^ without great suc- 

 cess, the clay being used raw and mixed with wood-ashes as a coun- 

 ter-shrinkage ingredient. No worse admixture, of course, could be 

 imagined, since the ingredient most desirable to avoid is thus di- 

 rectly introduced into the clay. 



IV. — TABLES OF ANALYSES OF WISCONSIN AND FOREIGN KAOLINS AND 



FIRE CLAYS. 



These tables are given so that a comparison between the Wis- 

 consin clays and the already well known clays of Europe and the 



