= 
Review of Dana’s Mineralogy. — 373 
We might extract largely from this portion of the work with 
profit to our readers, but our space confines us, and we must re- 
fer for fuller details to the volume, now easily accessible to all. 
Under crystallization by heat, we find the following new and im- 
portant observations, drawn from a practical source of the highest 
authority, and showing the importance of a close reunion between 
the theoretical and practical arts. 
_ “Tt has been supposed that complete fusion is necessary for the for- 
mation of crystals, or the crystallization of a mineral mass. But late 
observations have shown, that a high temperature without fusion, or 
even long-continued friction or vibration, will produce the same result. 
The tempering of steel is a familiar example. The coarseness or fine- 
ness of the grain, or, in other words, the size of the crystallizations, 
may be varied by the temperature, or the mode of tempering, and a bar 
that is almost impalpably fine, may in this way be changed to one con- 
sisting of crystalline plates an eighth of an inch in breadth. In these 
instances, the particles must have been free to move, as they are entire- 
ly rearranged into large crystals. Mr. N. P. Ames, of Springfield, 
Mass., who has observed numerous interesting facts bearing upon this 
subject, informs the author that if a bar of tempered steel, bent in the 
form of a semicircle, be heated on the inner side, when the heat has 
reached a certain point, the bar may easily be bent around, and made to 
curve in the opposite direction. He states that, until the moment when 
the requisite temperature is acquired, the bar does not yield; but at this 
moment a change takes place, which is distinctly felt in the hands, and 
the bar at once bends. He carefully measured the inner and outer 
curves of the bar, after thus bending it, and found them of the same 
length as before. This shows that there had been no compression of 
the particles on the inner side, which would have shortened that side, 
and therefore, also, that there was actually a removal of particles from 
the inner to the outer side. He observes, moreover, that the elasticity 
of the inner and outer sides was the same, which would not have been 
@ case, were the former compressed. By the old method of restor- 
ing a warped sword-blade, it was rendered unequally elastic, and would 
Spring more easily on one side than the other; but by the means here 
explained, the elasticity is perfectly equal on both sides. Here, then, 
there is a change in the position of the particles throughout the bar, 
Produced by a temperature very far short of fusion. The same exper- 
iment was often repeated, and he found that, at every time he bent the 
Steel, the temperature required was a little above that at which it bent 
the preceding time.’ 
— The change which takes place by friction or long-repeated concus- 
sion, is probably owing to the combined action of the heat thus excited, 
