LITHOLOGY. 



97 



of weight represents that of an equal volume of the 

 water, displaced by immersion. Therefore the weight 

 of the substance in air is to the loss of weight (i.e. 

 the weight of the water) as the specific gravity is to 

 unity consequently the weight in air, divided by the 

 loss, will give the required specific gravity. 



A delicate balance on a stand with minute weights 

 is required for the operation, one pan having a small 

 hook beneath from which the specimen to be tested' 

 is suspended by a fine platinum wire a few grains 

 of sand, added after the thread is attached, will 

 bring the scales into equilibrium. The actual weight 

 of the suspended object is first to be ascertained, then 

 there is placed beneath it a small vessel containing the 

 water in such position that it shall be completely im- 

 mersed during the second weighing operation. 



Reactions in the Wet Way. As a very useful addi- 

 tion to the particulars given under the head of " solu- 

 bility " in the table of tests, the foUowing list of " Ee- 

 actions in the wet way " has been copied from Paitley's 

 " Mineralogy," p. 22. 



Substances. 

 Carbonates. 



Sulphates. 



Reaction. 



Effervesce when treated with dilute 

 acids (either hydrochloric, nitric, or 

 sulphuric), owing to disengagement 

 of carbonic acid gas. 



Do not effervesce on the application of 

 acids, but when in solution, a drop 

 of chloride of barium will produce a 

 dense white precipitate of sulphate 

 of baryta. 



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