GYPSUM OR LAND PLASTER 599 



and other constituents of the filtrate, are determined by the usual 

 processes of mineral analysis. 73 



(2) State of Combination of the Lime. In a lime containing 

 only small quantities of magnesia the lime carbonate may be de- 

 termined by estimating the carbon dioxid by any one of the reli- 

 able processes in use. 74 In every case sufficient acid must be em- 

 ployed to combine with all the bases present. Tartaric or hydro- 

 chloric acid may be used. From the volume or weight of the 

 carbon dioxid obtained the quantity of calcium carbonate may be 

 calculated. Since magnesium carbonate is more easily decom- 

 posed by heat than the corresponding calcium compound, any 

 residual carbonate in a well-burned sample is probably lime. 

 The total percentage of lime in the sample is to be determined 

 in the usual way by precipitation as oxalate and weighing as 

 carbonate or oxid. The lime existing as oxid can be determined 

 by exposing a weighed sample in an atmosphere of aqueous vapor 

 until all the lime is slaked. After drying at 100 the increase in 

 weight is determined and the calcium oxid calculated from the 

 formula, CaO-f H 2 O CaO 2 H 2 . 



If now the total lime be represented by a; the lime combined 

 as carbonate by b ; and that present as oxid by c ; the quantity x 

 existing as hydrate may be calculated by difference from the equa- 

 tion 



x=a (b-\-c). 



The total lime as oxid and hydroxid may also be separated from 

 that present as carbonate by solution in sugar. 75 One gram of cal- 

 cium oxid is completely soluble in 150 cubic centimeters of a 10 

 per cent, sucrose solution. Magnesia, iron and alumina do not 

 interfere with the determinations. 



5O5- Gypsum or Land Plaster. This substance is highly prized 

 as a top dressing for grass and for admixture with stall manure 

 for the purpose of fixing ammonia. Its value in both cases de- 



73 Wiley, Principles and Practice of Agricultural Analysis, 2nd Edition, 

 1906, 1 : 402, 405, 434, 512. 



14 Wiley, Principles and Practice of Agricultural Analysis, 2nd Edition > 

 1906, 1 : 380, 436. 



75 Stone and Scheuch, Journal of the American Chemical Society, 1894,. 

 16 : 721. 



