On Superj)]Losj)hate of Lime. 



213 



theoretically required to produce the most perfect manure, and 

 what its composition would be when so made, it beln^ of course 

 understood that in practice it is not easy and not always desirable 

 to attain this end. But before doing; this it is necessary that I 

 should say a few words of sulphuric acid itself. Sulphuric acid is 

 known in commerce in two forms, both of which are solutions of 

 the true acid in water, differing from each other only in their 

 strength. Sulphuric acid, as it issues from the large leaden 

 cisterns or '^chambers" in which it is made, is not of the greatest 

 strength which it is possible to attain. But this acid, which is 

 known as brown " or " chamber " acid, is very largely consumed 

 for various manufacturing purposes. It can be concentrated by 

 boiling it down in glass or platinum vessels, and is then called 

 oil of vitriol." The brown acid and oil of vitriol differ as 

 before said in strength and also in density — the more the acid is 

 concentrated the heavier it becomes. In its most concentrated 

 form it is onl}^, however, a solution of sulphuric acid — the real 

 chemical compound sulphuric acid being unknown to commerce. 

 In the remainder of this paper in speaking of real sulphuric acid 

 I must be understood to mean the chemical substance, of which 

 in oil of vitriol and chamber or brown acid we have only solu- 

 tions of differing strengths. The strength of solutions of sul- 

 phuric acid is easily ascertained by finding their density, which 

 can be done by any person by the aid of little glass balls or beads 

 sold by the philosophical instrument makers ; and as it is impos- 

 sible to judge with any accuracy of the strength of the acid by its 

 appearance, no person who attempts to make superphosphate of 

 lime for sale^ and indeed no farmer who makes it for his own use 

 to any very considerable extent, should fail to take advantage of 

 this simple means of ascertaining the strength and purity of the 

 material which he is using. At the end of this paper I shall 

 place a table constructed by Dr. Ure, which shows the quantity 

 of real acid contained in solutions of sulphuric acid of different 

 densities, and which will be found useful to those who may not 

 have access to treatises on chemistry. By reference to this table 

 it will be seen that the strongest oil of vitriol, of specific gravity 

 (or density) 1-8485 (water being 1-000), contains in 100 parts 

 81-5- parts of real acid. *The brown or chamber acid is much 

 weaker and of course lighter — its density is usually from about 

 1-600 to 1 700, and every 100 parts, at 160 sp. gr., contain 58, 

 and at 1*70 contain 64^^ parts of real acid. By the first column of 

 the table we see that acid of this latter strength may be looked 

 upon as a mixture of 79 parts of oil of vitriol and '11 parts of 

 water. 



These few remarks may perhaps sufBce to enable us to calcu- 

 late the quantity of either of these acids that it may be necessary 



