LIME INJURED BY EXPOSURE TO AIR. 



245 



On the vnprovemenl of Drills, hj hammer-hardening them cold. 



Mr. Andrew Prltchard, the inventor of the hard-shell lac cement, 

 finding that steel, when hardened and tempered, is susceptible of 

 receiving the condensing efFect of the hammer ; has applied it, 

 with considerable advantage, to the points of small drills, by ham- 

 mering them upon their ilat surfaces. 



On improving the Edges of Square Broaches, or Boring-bits, by 

 Haminer-hardenhig them. 



Mr. Joseph Clement, an excellent workman, and mechanical 

 draughtsman, informed the Editor, since the publication of Mr. 

 TurreiTs great improvement in gravers, that a friend of his in 

 Scotland, many years since, improved the quality of his square 

 broaches, by hammer-hardening them cold, after being hardened 

 and tempered upon their flat sides. He, however, kept this pro- 

 cess nearly a secret. 



The Editor thinks it would have been much better to have, ham- 

 mered them upon their angles, as Mr. TurreU does his gravers, 

 which would have had a much better condensing eflfect ; and then 

 to have ground them again, to bring up the blunted edges to their 

 proper figure for use. ""The tive-square broach is also equally sus- 

 ceptible of improvement in this way. [Tech. ReposHory. 



Experiments showing how quickly Lime imbibes Carbonic Acid Gas, 

 and is injured by Exposure to Air : Practical Inductions, ^c. 

 On the 22d of August, 1776, I exposed two pounds avoirdupois 

 of well-burned nonetfervescent chalk-lime, in fragments of the stze 

 of a walnut, spread on a board, in a dry unfrequented room. I 

 exposed the same quantity of this lime, at the same time and in the 

 same manner, in a passage through which there was a constant cur- 

 rent of air 5 and I put the same quantity of this lime, in fragments 

 of the same size, in a box which might hold as much 'foveoi it, 

 and placed the box loosely covered with its hd, close by the hrst 



portion of lime. r , r ^ i 



In twenty-four hours, the superficial lumps of the hrst parcel 

 cracked in some parts a little, those of the second cracked more, 

 those of the third were not visibly altered. In forty-eight hours, 

 the first parcel cracked so much as to fall into smaller fragments 

 on bein^ moved, and these were reducible to powder by pressing 

 them between the fingers : The second parcel underwent the like 

 or rather a greater change, fov it was more cracked and triable : 

 The third now begun to crack in the superficial parts. 



On weighing them, I found that the first parcel weighed 2 lbs. 

 5 oz., the second, 2 lbs. 6 oz. I dr., the third, 2 lbs. 1 oz. 10 drs. : 

 1 then returned them to their former stations. 



In six days, the first parcel weighed 2 lbs. 10 oz. 7 drs. 5 the se- 

 cond, 2 lbs. 12 oz. 1 dr. ; the third, 2 lbs. 4 oz. 8 drs. 



In twcnty-one days, the first parcel weighed 3 lbs. 1 dr. ; the 

 second, 3 lbs. 2 oz. 1 1-2 dr. ; the third, 2 lbs. 6 oz. 8 drs. 



