404 



GEOLOGY OF EASTERN WISCONSIN. 



portions indicated, the two best commercial cements being taken as a 

 standard of comparison, and expressed by 100. It will be observed 

 that the average of the tests of the Wisconsin product, exceeds the 

 highest of the commercial articles by 23 per cent., and exceeds the 

 average of the eleven, which represent the relative strength of the ce- 

 ment in the Milwaukee market, by 54 per cent. The remarkable im- 

 ported cement, known as Portland, was included in these tests, and the 

 results are given in the table. As it is extensively used in Europe, 

 and has been submitted to a great many trials, its character and value 

 are well known to engineers and experts, and it therefore furnishes a 

 valuable standard of comparison. Within the proportions named 

 above, the Wisconsin cement surpasses the best of the commercial 

 cements almost as much as it is surpassed by this unrivalled artificial 

 European product. 



It remained to test the adhesive strength of this mortar, and for 

 this purpose Mr. Whittemore joined common brick crosswise with 

 mortar composed of equal parts of cement and sand, and kept them 

 under a pressure of five pounds per square inch, until the mortar had 

 set, when the brick were packed in damp sand for seventy days, and 

 then were separated by tensile strain, with the following results: 



Commercial cement No. 1 39% 



Average of three products of Milwaukee cement 75% 



English Portland 47% 



In many instances, the result only shows the cohesive strength of 

 the brick, since after a strain of 60 pounds is reached, the brick is of- 

 ten ruptured instead of the mortar. 



Sawn slabs of marble treated in a similar manner showed an adhe- 

 sive strength of 53f pounds, when joined 96 days. The rate of indu- 

 ration was ascertained by crushing cylinders composed of equal parts 

 of cement and sand, at the end of every five days up to ninety. The 

 following series indicates the strength, in pounds, per square inch, 

 attained, beginning at the age of five days and ending at ninety: 403, 

 837, 1,178, 1,519, 1,953, 2,418, 2,635, 2,759, 2,867, 2,976, 3,068, 3,162, 

 3,255, 3,332, 3,410, 3,487, 3,571, 3,658. 



