Mr. A. Liversidge on Supersaturated Saline Solutions, 69 



cotton- wool included, inactive, the steam escaping through the inter- 

 stices of the cotton and not affecting the spirit. When cold a drop 

 of the spirit or acid was delivered by merely heating the glass bulb. 



Exp, Trial was next made of several solid dehydrating substances, 

 such as calcic chloride, anhydrous chromic acid, phosphoric anhy- 

 dride, freshly ignited quicklime, &c. 



These bodies were placed in sealed thin glass bulbs and heated 

 nearly to redness and then dropped into the supersaturated solution ; 

 the flasks were plugged with cotton-wool, through which a glass rod 

 passed, and boiled up, after which they were allowed to cool for some 

 hours ; when quite cold the bulb was broken by means of the glass 

 rod and its contents set free, but, as in the case of the liquid, with 

 no result. 



It should perhaps here be mentioned that each flask was always 

 proved to be thoroughly supersaturated by dropping in a crystal of 

 the salt or touching the solution with a dirty rod, after the sub- 

 stance made trial of was found to be wanting in nuclear power. 



From the foregoing it appears that the crystallization of super- 

 saturated saline solutions is not determined by the removal of water 

 by chemical agency; neither do porous bodies, like wood, charcoal, 

 sponge, spongy platinum, earthenware, &c, determine the solidifi- 

 cation of solutions by mechanical absorption of the water. 



Concerning the action of thin films. 



In the same paper it is stated that while oils, fats, and greasy 

 bodies generally do not act as nuclei when chemically clean and in 

 the bulk, i. e. in the form of a solid mass, lens, or drop, yet these 

 identical bodies when in the form of thin films do act as nuclei, and 

 that any substance which possesses a nuclear action has derived 

 such power from having become contaminated with a thin film of 

 greasy matter, which it acquires by handling, wiping with a dirty 

 cloth, or by mere exposure to the air containing the products of 

 respiration and other excretions, &c. 



Thus in the series of experiments detailed it was found that such 

 bodies as ether, absolute alcohol, naphtha, turpentine, herring-oil, 

 sperm-oil, castor-oil, and many others, while in the form of a lens 

 or globule, did not act upon a supersaturated solution, but did im- 

 mediately when spread out into a thin film. 



It should be noticed that the oil was added to the solution by 

 removing the cover of the flask, delivering the drop, and then repla- 

 cing the cover ; or a glass tube was used provided with a shield cover- 

 ing the mouth of the flask : both methods have the great objection 

 of exposing the solution to the air, and so allowing nuclei to gain 

 access. 



It is stated that if the finger be cleaned by washing it in alcohol 

 or caustic potash, or by passing it through the flame of a spirit-lamp, 

 it may be held in a supersaturated solution for some time witl out 

 causing crystallization — but that if it be rubbed against the sides of 

 the flask, a greasy smear is produced which at once acts. 



The writer has repeated this form of experiment several times, but 



