Polytechnic Association. 775 



Cost. 



The total cost of one cubic foot of finished building block varies 

 from seventy-nine and one-half cents to eighty-four and one-half cents 

 If, however, large pebbles and small cobble stones are incorporated 

 into the mixture, the price may be reduced ten or fifteen cents per 

 cubic foot. For these reasons, the Sorel system has been limited in 

 its application to articles like soap-stone stoves, whetstones, medal- 

 lions, emery wheels, window caps, sills and other articles of small 

 bulk and great relative value. 



" For the peculiar purposes to which it is adapted," says General 

 Gillmore, " it supplies what has heretofore been felt a great want, 

 and in this field, which is neither narrow or unvaried, it has no 

 prominent rival." 



Prof. J. Phin suggested that in making not only artificial stone, 

 but mortar, it is important that the sand should be sharp ; and as 

 common sand is, much of it, rounded, it might be advantageous,to use 

 quartz stamped or crushed into fine particles, instead of sand. 



The President remarked that the specimens exhibited were very 

 much softer than natural stone. 



Adjourned. 



January 26, 1872. 



Prof. S. D. Tillman in the chair ; Robert Weir, Esq., Secretary. 

 Water Gauge. 



Mr. George R. Osborne exhibited and explained a model of a new 

 water gauge for steam boilers, by which the height of the water in 

 the boiler may be indicated at a distant point, and at a different level 

 from that of the boiler. The gauge itself contains a large bent tube, 

 containing mercury in the two legs, . standing at an equal height 

 when the water in the boiler is at the desired level. One end of the 

 tube is bent again, and reduced in size in the descending leg, con- 

 taining a colored fluid lighter than water, to multiply and make more 

 conspicuous the changes in the mercury, and attached to this is a 

 graduated scale. The lower end of this tube is filled with water, 

 and connected with the water in the lower part of the boiler ; and 

 the other end of the tube, also filled with water, is connected with a 

 perpendicular tube within the boiler, the top of which rises nearly to 

 the top of the boiler. The steam pressure acts equally upon both 

 surfaces of the mercury in the syphon ; but if the water in the boiler 



