246 farmers' and mechanics' journal. 



During this increase of weight, the fragments spht into smaller 

 pieces, but did not fall into powder, except in a small part of them, 

 or when they were handled. 



By similar experiments made on well-burned stone-lime, 1 found 

 that this imbibes matter from the air nearly in the same manner as 

 ehalk-lime, but rather more slowly ; which I think is owing to its 

 closer texture. 



On exposing common chalk, or stone-lime, in the same way, I 

 find that it increases in weight much less and more slowly. 



To discover the quantity of water which the lime imbibed from 

 the air, and which contributed to this increase of weight, 1 put each 

 parcel in a glass retort ; and adjusting to it my apparatus whereby 

 all that is condensible is saved, whilst elastic fluids are at liberty to 

 escape, I found that the quantity of water contained in each parcel 

 of lime, was nearly in some, and in others accurately l-24th of the 

 gained weight, the remainder of the weight gained was of carbonic 

 acid gas mixed with a little air, which latter 1 do not reckon, be- 

 cause it was already weighed in the lime. 



If a glass bottle be filled with fragments of well-burned chalk- 

 lime, or stone-linfic, or shell-lime, and well stopped with a ground 

 glass stopple slightly waxed where it fits the neck of the bottle, 

 the lime will remain unaltered in weight, or in any other known 

 particular, for a year or two ; as 1 have repeatedly experienced : 

 even the phosphorescence of lime is thus preserved in its full 

 lustre, for a year or more. 



Thus it appeared that well-burned lime imbibes carbonic acid 

 gas from the air, the sooner, as it is the more fully exposed to it : 

 that lime imbibes this matter from the open air, the more greedily 

 as it is more perfectly deprived of it previous to the exposure : 

 that lime cannot be long preserved unaltered in any vessels which 

 are not perfectly air-tight, but may be kept uninjured for any time 

 in air-tight vessels filled with it : that chalk-lime, by reason of its 

 sponginess, or by some other condition of it, requires to be kept 

 less exposed than stone-lime, and well-burnt lime less exposed than 

 common lime, to render the depravation of them equal in equal 

 times : that if carbonic acid gas imbibed by lime previous to its 

 being used in mortar, be as injurious to the mortar, as the carbonic 

 acid gas retained in equal quantity by ill-burned lime is, lime grows 

 the more unfit for mortar every hour that it is kept exposed to air, 

 whether in a heap, or in casks pervious to air. 



I think, moreover, (hat these experiments show that lime under- 

 goes these changes by expos'jre, much quicker than has been sus- 

 pected ; since well-burned chalk-lime kept in a dry room, imbibes 

 near a pound of carbonic acid gas in three weeks, in the summer 

 season. 



Not to trust to theory what I could prove by experiment, I did 

 not rest satisfied with the observations and reasons which might 

 persuade one, that lime, which has imbibed some carbonic acid 

 ,gas, is as unfit for the uses now under consideration, as lime which 



