312 Dr Ogden on Saline Crystallization. 



mediately excite crystallization ; and this may readily be suppo- 

 sed to result from the entrance of the air. But supposing that 

 there can be no suspicion of such an inaccuracy on the part of 

 the operator, the agitation produced by the entrance of the aU^ 

 may, of itself, be a sufficient cause. The violence of the atmo-* 

 spheric vibrations caused by the discharge of a pistol is sufficient 

 to break ordinary window-glass. Every one knows the loud re- 

 port occasioned by puncturing the concave bladder forming the 

 upper surface of a vessel exhausted by the air-pump. Of the 

 same character is the sound in the common operation of opening 

 a bottle of wine. The effervescence of champagne by a smart 

 blow on the top of the glass with the palm of the hand, is a fa- 

 miliar illustration of a change in the constitution of a liquid, 

 occasioned by a violent shock. In like manner, the concussion 

 produced on the surface of a supersaturated liquid, by the sud- 

 den admission of air, may be amply sufficient to induce crystal- 

 lization. 



Besides the circumstance of pressure not being essential to 

 crystallization, nor certain to produce it, there are other minor 

 points in the nature of supersaturated solutions, into which I 

 was led to inquire, and which it may not be deemed irrelevant 

 to mention. These, as well as the first, will be sufficiently ex- 

 plained by the following desultory experiments. It is necessary 

 to premise, that, in all cases, the solutions were unprotected 

 from atmospheric pressure, except where the contrary is express- 

 ly stated. 



1. A hot solution of carbonate of soda nearly saturated, and 

 contained in a six-ounce phial, was allowed to stand in a hot 

 sand-bath until the whole was cool. Twenty-four hours after- 

 wards it was perfectly fluid, but being gently moved, it solidi- 

 fied. 



2. A strong solution of sulphate of soda was filtered whilst 

 hot into two phials, one of which was corked immediately, and 

 the other was left open. At the end of three hours, the contents 

 of each remained fluid, and each became solid on being agitated. 



3. A strong solution of sulphate of soda was filtered whilst hot 

 into an open jar three inches in diameter. Twenty-four hours 

 afterwards, it remained perfectly fluid. A crystal of the same 

 salt being dropped into it, the whole solidified in a few seconds. 



