on the Principle of Cementitious Aicnileclure. 267 



Siidly. Four of the soundest seconds were selected, which 

 broke with pounds as follows: 



605. 617. 719. 605. = 611 mean. 

 Srdly. Some of the commonest bricks were tried, but the 

 strength was so very unequal that it precludes any dependence 

 on this kind of brick. 



Common bricks: 84. 394-. 50. 125. 30. &c. 

 Pipes. — A pipe 8 inches internal diameter, and made of 

 radiatedbricks joined with cement, the bricks with an internal 

 coating of cement, making the thickness 3 inches, was sto))ped 

 at both ends, and by means of a pipe attached to it was filled 

 with water and burst by a forcing-pump, having a column of 

 mercury rising in a glass tube to indicate the force employed. 

 It sustained a pressure of <\:2 inches, (equal to a column of 

 water 47 feet high,) and then burst. 



The bricks used in this pipe were very sound and hard, as 

 was also the cement; and had it been properly applied, a much 

 greater force would have been necessary to break the pipe ; 

 — so that this experiment shows the negligence in constructing 

 it, and not the strength of brick and cement. The pipe had 

 been made for years. 



At the beginning of February 1812, some pipes were made 

 of three measures of cement and two measures of sand, 8 

 inches internal diameter, 2 inches thick, and 5 feel long; the 

 thickness was not indeed uniform, owing to accidents in the 

 making; but this wnll be noticed in relating each experiment. 

 At the beginning of May following, some of them were burst 

 by the means above mentioned, having the tube of mercury 

 attached. 



The first pipe tried sustained a momentary pressure of 70 

 inches, but it afterwards burst with 56 inches mercury, = 63 

 feet water; it broke from top to bottom, having a very straight 

 crack on one side only, and there the thickness was 1-6 inch. 



A second pipe burst with 42 inches mercury, and the frac- 

 tured part was 1*75 inch thick. 



A third burst with 47 inches mercury, and the thinnest 

 part was 1'8 inch thick. 



In January 1812, a round brick tank was made, 41 inches in 

 diameter and 42 inches deep, of the thickness only ol' a brick 

 thick, i. e. 2\ inches, with an internal coaling of cement half 

 an inch thick; a brick head was made to it, so that evtM-y part 

 was water-tight. In ]\Iay following it was tried by the forcing- 

 pump, when the head (which might have been expected to 

 give way first, as the obstacles in putting it on did not admit 

 the cement to be properly applied) parted Irom the sides with 



17 inches mercury. 



2 M 2 Spccipc 



