518 APPENDIX. 



Its atomic weight is 1 4*75, containing 5 of sulphuric acid. I 

 say, therefore, 



14 '75 : 5 : : 150 : 50-847 = sulphuric acid in 150 grains of sul- 

 phate of barytes. 



For sulphate of barytes, which is a calculation of perpetual re- 

 currence in the laboratory, a good method is, to have a part of 

 the process ready finished, and lying at hand for use. This 

 may be done in the following way : 



The logarithm of 5 is . . 0*6989700 



Subtract the log. of 14-75 . . 1-1687920 



Remains . . . 1-5301780 



This constant logarithm is to be added to the logarithm of the 

 quantity of sulphate of barytes of which you wish to know 

 the sulphuric acid. In the present example the quantity is 

 1 50 grains. 



Logarithm of 150 . . . 2-1760913 



Add , 1-5301780 



Sum .... 1-7062693 



Now, this is the logarithm of 50 f 847> the quantity found 

 above. 



Second example. Suppose I have a solution containing 240 

 grains of nitrate of silver, and that I want to know from the 

 tables how much common salt will just precipitate the whole 

 of the silver. We see from the second table that the atomic 

 weight of nitrate of silver is 21-5, and that of common salt 7-5. 

 We say, therefore, 



21-5 : 7-5 : : 240 : 83-72 = the weight of common salt required. 



Third example. Suppose I have a solution of 90 grains 

 of oxalic acid crystals, and that I wish to know how much bi- 

 carbonate of potash will be necessary just to saturate the acid. 



