. BUILDINGS IN INDIA. 



It however the clay be hardened by being converted into a 

 vitrified, or otherwise solid brick, then indeed it ceases to be 

 under the dominion of frost, and is at all events, I should ^-up 

 pose, as good as so much sand. It remains to be enquired by 

 chemical investigation, whether some affinity between clay, 

 thus hardened, and lime docs not exist, which expelling in their 

 union their caloric, combines the two substances more intimately 

 and in a smaller compass, than that of lime mixed with sand ; 

 and, of course, gives to the compound more hardness, and 

 permanent continuity. If such affinity does exist, which I will not 

 deny, such brick dust is so far superior in quality, as an ingre- 

 dient of cements, to sand. But it is, I think, far counterbalanced 

 by its other quality of infinite contractibility and expansion. Clay, 

 in its purest state, is used in Wedge wood's pyrometer, on account 

 of this very quality, which it appears never to lose; and from 

 thence arises the perfection of this most useful instrument. 

 When the cement, of which brick dust is an ingredient, is laid 

 on in a moist state, it occupies in some cases (for I have last 

 year had much unpleasant experience of the fact in the floors 

 laid in Deniroth's cement at Washington) 4- more space than 

 when dry. On a wall exposed to heat, or upon a timber floor 

 accessible, and at first pervious to the air, there appears to be a 

 limit to the contraction of the cement. But in a heavy vaulted 

 building, like the Capitol of the United States, at least, the 

 moisture of which evaporates slowly, I would reject brick dust 

 altogether as an ingredient of any kind of cement, either for 

 mosaic floors, terraces, or facings. Full justice appeared to be 

 done by the contractor and patentee, in beating his floors both as 

 to time and labour, but after a year's drying they have cracked 

 uito innumerable fissures. 



From what I have said, it will be evident, that I consider 

 brick dust as an ingredient in cements, inapplicable to our cli- 

 mate and of course useless. 



Good clean washed sand, and stone lime, in the proportion of 

 three of sand and one of lime, up to six to one, according to the 

 size of the particles of sand, and the goodness of the lime, is a ce- 

 ment that will never fail, if well mixed and worked, and laid 

 on as soon as possible after being mixed. The lime in slack- 



