230 Analysis of Soils. [Oct., 



and then add an excess of black oxide of mercury to the solution, 

 and boil in a platina capsule. Then dissolve out the alkalies 

 and filter the solution. The magnesia is thrown down by the 

 oxide of mercury, and by driving the mercury off by heat we ob- 

 tain the magnesia which is to be converted into a sulphate by 

 sulphuric acid, heated to redness and weighed. 



We can also analyze the insoluble silicates by driving off the 

 silicious matter by the acid of fluorine in the state of fluo-hydro-si- 

 licic acid gas. This is done by mixing the finely pulverized sili- 

 cate with fluor spar, and placing it in a platina crucible, adding 

 pure sulphuric acid (Nordhauren) which decomposing the fluoride 

 of calcium, disengages fluorine in combination with hydrogen, and 

 carries off the silicic acid in vapor or gas. We heat gradually 

 to redness to drive off the sulphuric acid. When the silex is re- 

 moved M^e dissolve the soluble sulpliates in w^ater, and most of 

 the sulphate of lime remains insoluble. We remove the remainder 

 of the lime salts with the alumina by adding first ammonia in 

 excess, and then oxalate of ammonia. The sulphates of the al- 

 kalies and of magnesia only remain in the solution, from which 

 they are separated as before described. 



Having completed the analysis of the insoluble silicates, we 

 have now to return to the more complete separation of the ingre- 

 dients obtained from the first solution. Alumina and per-oxide 

 of iron, oxide of manganese, with phosphate of alumina and iron, 

 may be found in that precipitate. The quantity of the precipitate 

 is too small for the quantitive determination of all the ingredients 

 above mentioned, but we can make the qualatative examination, 

 and then by operating on another and larger lot of the same soil, 

 we may obtain a suflBciency for a more thorough analysis. 



We may then dissolve the 5 grains of alumina, per-oxide of 

 iron, &c., in chlorohydric acid, and dilute with pure water. 

 Take a portion of the solution and add ammonia in excess, which 

 will reprecipitate the alumina, per-ox. iron, &c. Collect the 

 precipitate on the filter, and wash it; remove it to a capsule by 

 means of a platina spatula, treat the gelatinous precipitate with 

 acetic acid, which will dissolve all but the phosphates of alumina 



