172 Mr. D. Campbell on the Action of the Soap-Test 



the degrees of hardness of the water as ascertained by the soap- 

 test, this being the rule given by Professor Clark in a private 

 circular to his chemical friends to "infer the degrees of hard- 

 ness from an ordinary analysis." But in this I was mistaken. 

 I therefore thought it advisable to make some experiments 

 with the soap-test upon water of which I knew the actual 

 composition. 



The soap test I employed in the following experiments was 

 prepared with the utmost care, the alcohol having always been 

 digested with carbonate of potash for many hours before being 

 reduced to proof-spirit. The soap corresponded with what 

 Prof. Clark advises, nearly 1 oz. in a gallon of proof-spirit, 

 giving a soap-test, thirty-two test measures of which formed a 

 perfect lather with 100 like measures of a standard solution 

 of 16° hardness of lime 5 which remained all over the water for 

 five minutes when first placed after shaking, and which could 

 be renewed at any time by again agitating it. The soap-test 

 was likewise proved by standard solutions of lime of 12°, 8°, 

 6°, 4°, 2° hardness. 



The distilled water employed in making standard solutions 

 was selected with much care, and tested in various ways to be 

 sure of its purity. 



The first experiments which I made were upon water con- 

 taining a salt of magnesia in different proportions. 



To prepare such solutions, 192 grains perfectly pure and 

 dry sulphate of magnesia (MgCX, S0 3 ), which is the equiva- 

 lent quantity of that salt to 16 grains carbonate of lime, were 

 dissolved in a gallon of distilled water. This was considered 

 as a standard of magnesia equal to 16° hardness of lime, or a 

 standard of magnesia equal to 16°. Fifteen other standard 

 solutions were prepared from this, as follows: by taking one 

 measure of the 16° standard, and adding fifteen like measures 

 of distilled water to it, we have a standard of 1° magnesia; 

 with two measures of original standard and fourteen like mea- 

 sures of distilled water added to it, we have a standard of 2° 

 magnesia; and so on up to 15°. 



The results which I obtained (see Table No. 1, p. 173) 

 when treating these solutions with soap-test, were such as to 

 induce me to proceed with experiments upon mixed standard 

 solutions of magnesia and lime. These I prepared as follows: — 

 Magnesia standards ranging from one to sixteen were made 

 each to contain double the amount of the magnesian salt that 

 the previous standards contained. Lime standards were then 

 made of 3'2°, 24°, 16°, 12°, 8°, 4° hardness in a gallon. When 

 fifty measures of these lime standards were mixed with fifty 

 like measures of the last magnesian standards, I then consi- 



