THE ACTION OF FROST IN WATER-PIPES. 307 



tain saline solutions exert at the moment of crystallization, 

 he could conveniently imitate the action of freezing with- 

 out the aid of natural or artificial frost. Epsom salts, 

 nitre, alum, sulphate of iron, Glauber's salts, etc., were 

 tried. The last named, Glauber's salt (or sulphate of 

 soda), which is very cheap, was found to be the best for 

 the purpose. 



His method of applying the test is as follows: Cut the 

 specimens into two-inch cubes, with flat sides and sharp 

 edges and corners, mark each specimen with a number, 

 either by ink or scratching, and enter in a book all particu- 

 lars concerning it. Make a saturated solution of the sul- 

 phate of soda in rain or distilled water, by adding the salt 

 until no more will dissolve; perfect saturation being shown 

 by finding, after repeated stirring, that a little of the salt 

 remains at. the bottom an hour or two after the solution 

 was made. Heat this solution in a suitable vessel, and 

 when it boils put in the marked specimens one by one, and 

 keep them immersed in the boiling solution for half an 

 hour. Take out the specimens separately and suspend 

 them by threads, each over a separate vessel containing 

 some of the liquid in which they were boiled, but which 

 has been carefully strained to free it from any solid parti- 

 cles. In the course of a day or two, as the cubes dry, they 

 will become covered with an efflorescence of snow-like crys- 

 tals; wash these away by simply plunging the specimen into 

 the vessel below, and repeat this two or three times daily 

 for four or five days or longer. The most suitable vessel 

 for the purpose is a glass " beaker," sold by vendors of 

 chemical apparatus. 



In comparing competing samples, be careful to treat all 

 alike, i.e., boil them together in the same solution, and dip 

 them an equal number of times at equal intervals. 



Having done this, the result is now to be examined. If 

 the stone is completely resistant the cube will remain 

 smooth on its surfaces and sharp at its edges and corners, 

 and there will be no particles at the bottom of the vessel. 

 Otherwise, the inability of the stone to resist the test will 

 be shown by the disfigurement of the cube or the small 

 particles wedged off and lying at the bottom of the liquid. 



