386 LATROSE.S OBSERVATIONS 



the mortar, but that it continues to contract, and to require 

 forcible compression by beating or rubbing until it is quite dry, 

 it become?, on more than one account, a very noxious as well 

 as a very inconvenient ingredient in all cements, to be used, 

 where there is frost, and where labour is dear. 



I should be obliged to write a voluminous treatise on this 

 subject, were I to submit to you all that my experience, as well 

 as my reasonings suggest, to counteract the prejudice in favour 

 of the use of brick dust in cements north and south of the tro- 

 pics. Its utility beyond the reach of frost, I need not examine. 

 It would be useless to establish or to refute it in our region of 

 severe winter. I will therefore only endeavour to comprize, in 

 as small a compass as possible, what may be useful to our own 

 citizens. 



Belidor, Blondel, Sturm, Smeaton, Higgins, Adams, and 

 many other French, German, English and Italian writers have 

 all recommended brick dust in some cement or other. I have 

 none of their works at hand, so as to refer to their receipts or then- 

 experiments, and no doubt their cements have possessed all the 

 qualities ascribed to them, when the brick dust has been pre- 

 pared of well burned bricks. I have also seen brick dust em- 

 ployed by engineers and architects whom I have personally 

 known, and have employed it myself; but I do not recollect 

 a single instance of the cement in which it has been used hav- 

 ing resisted the effect of moisture and frost. Natural argillaceous 

 stones are more apt to be forced to pieces by frost than any 

 others.* Bricks not sufficiently burned are always destroyed 

 by frost. The effects of frost on the natural clay of the earth is 

 well known, — it renders our roads almost impassable in spring. 

 It seems therefore, to plain sense, a conclusive argument against 

 the use of this material in cements, that wherever we see it pre- 

 sent in anv natural or artificial production, its dissolution by 

 frost is certain. 



* The freestone of Acquia, however, appears to be sand cemented by an alluminous (ar- 

 gillaceous) infusion. Some of it is dissolved by the frost, but the best stone resists it most 

 perfectly. Water oozing through this stone covers the face of the rock with allum. I have 

 not been able to detect in this sand stone any particle of calcareous matter. Its smell when 

 moist is strongly earthy. See my memoir in the Philosphical Transactions, on this stone. 

 page 283 of this Volume. 



