Mechanical Science. 149 
2nd. About four pints of common cold water is to be saturated 
with sulphate of soda, so that a few grains of the salt shall remain 
undissolved. 
8rd. This solution is to heated to ebullition, and then all the 
cubes to be entirely immersed in it. When the boiling has recom- 
mencéd it is to be continued for half an hour. 
4th. The cubes are to be withdrawn from the solution and 
placed each one in a saucer, numbered as the cube is; a small 
quantity of the solution is to be poured on to each cube, and the 
whole left until covered with white efflorescences perfectly analo- 
gous in appearance to the rime or hoar frost, which causes the dis= 
integration of the stones. These efflorescences will appear in 
about twenty-four hours if the air is dry or hot, but in a humid 
atmosphere are sometimes five or six days. 
5th. When the efflorescences appear on the angles and sides of 
the cubes, they are to be dissolved again by means of a few drops 
of water, or better still with a little of the solution in which the 
cubes were boiled. If well managed the efflorescences will soon 
re-appear, and when well formed, are again to be removed ina 
similar way, and this is to be repeated for three or four days toge- 
ther *; after which each cube may be washed with abundance of 
common water, but without removing it from the saucer. 
6th. The specimens to be tried having been washed on all their 
faces, the detached matter is to be examined, and a judg- 
ment formed from it, of the relative qualities of each kind of 
stone submitted to the proof: for the greater the number of the de- 
tached particles collected in the saucer, the more liable is the 
stone to be attacked by frost; the smaller the number the more 
capable is it of resisting the action. 
As yet, all the results of this test have accorded perfectly with 
the effect of time and frost. Such stones as have been found to 
disintegrate by frost have given way to the salt, such as time has 
sanctioned have resisted the new agent, so that the mechanical 
effects of the two are perfectly analogous, Crystallization takes | 
place with both, augmentation of volume, efforts on the surfaces 
of the small cavities containing the water or solution, and if the 
aggregation be not sufficiently powerful to resist the action, dis- 
ruption, and a gradual decay of the rocks either in their natural 
sites, or if they have been applied to use in their new situations. 
The action of the sulphate of soda being quite mechanical, is ex- 
erted indifferently on all kinds of rocks deficient in aggregation, 
on limestones, sandstones, large grained granite, granites of too 
micaceous a structure, shists, lavas, &c. It may be employed as 
a proof or test also even upon slates, bricks, tufas, mortars, and 
cements, as is proved by a table of various results of this kind. 
* If the proof be continued for a longer ames good building stones may be 
rejected, for the prolonged action of the salt is more powerful than that of ice, 
