266 A GENERAL FORMULA FOR THE 



convert it into sulphate, by adding sulphuric acid to a slight 

 excess, and then exposing to a full red-heat. r J he dry sul- 

 phate of lime will remain, 100 grains of which contain 41.5 of 

 lime *. 



The next step is to precipitate the magnesia. With regard 

 to this there is some difficulty, particularly as connected with 

 the design of the present formula. The principle on which it 

 is founded is, first, to remove all the acids but the muriatic, 

 and, secondly, to remove the bases, or otherwise estimate their 

 quantities. The lime and the magnesia may be removed by 

 precipitation ; the soda cannot. The process, therefore, must 

 be so conducted, as to leave it at the end in the state of mu- 

 riate of soda. Hence it is necessary either to remove any new 

 product introduced in the previous steps of the analysis, or if 

 any such remain, to be able to estimate its quantity with pre- 

 cision. In decomposing the muriate of lime by oxalate of am- 

 monia, muriate of ammonia is substituted, which can be after- 

 wards dissipated by heat. The object, therefore, is to decom- 

 pose the muriate of magnesia, and remove the magnesia, either 

 by some similar method, or, if not, by some other in which the 

 muriate substituted can be accurately estimated ; and to attain 

 one or other of these conditions, gives rise to the difficulty to 

 which I have alluded. 



The 



* The only source of error to which this step of the analysis is liahle, is that 

 which will arise if more barytes has been used in the first operation, than 

 was necessary to precipitate the sulphuric and carbonic acids. It will be 

 thrown down in the state of oxalate of barytes, and be converted into carbo- 

 nate and sulphate, and thus give the apparent proportion of lime too large. 

 This is obviated, of course, by taking care to avoid using an excess of bary- 

 tes. To render the operation of the oxalate of ammonia as perfect as possible 

 in precipitating the lime, the water should be considerably reduced by evapora- 

 tion, taking care to avoid any separation of any of its ingredients. 



