Factitious Puzzolana . 
position of inclosures, or for light roofs. Bridges of a 
single arch may be formed with it; and I have seen 
it adhere so strongly to glazed tiles, that it was neces- 
sary to break the tiles to detach it. 
The puzzolana proper for constructions beneath the 
water, forms the most solid body in it. Three months 
after immersion it is an actual stone capable of receiv- 
ing a polish. The lime in it is always regenerated into 
carbonate of lime in ten weeks. 
When it may be thought by any one that he has been 
deceived as to the certainty of these effects, it will al- 
ways be found, that he either has not observed the quan- 
tities directed of the puzzolana and the lime, or that 
lie has used the reverse of that kind of the cement pro- 
per for the work. w 
I commonly used lime in the state of impalpable pow- 
der, slacked in Lafaye’s manner, for works exposed to 
the air; and employed lime in the state of putty , for 
works which were to be covered with water. Some- 
times I used lime in powder for the same work. This 
difference depends on the degree of goodness of the 
lime, on its greater or lesser richness, or its proportional 
poverty. Custom gives the advantage of knowing the 
different kinds on mere inspection. 
The use of lime in powder appeared to me to merit a 
preference in the preparation of mortars or cements. I 
prepared my factitious puzzolana in a certain quantity as 
soon as I knew the proper proportion of the lime ; and I 
had thus the advantage of being able to work it in 
troughs in the same manner as sulphate of lime. The 
whole was well mixed together and put into sacks ; by 
which means the masons had nothing to do with the 
mixture of the articles, (which is too often left to unprin- 
cipled workmen,) and being thus master of the respective 
