§ 124. MISCELLANEOUS DETERMINATIONS. 245 



III. or lY., § 94, with these exceptions, that sulphuric acid 

 need not be determined under a, and that, before precipi- 

 tating lime by ammonic oxalate, the barium should be 

 removed by precipitation with a very dilute sulphuric 

 acid, containing but one part of acid in 300-400 of water ; 

 the precipitated baric sulphate should be examined for 

 lime by heating the moist precipitate with ammonic car- 

 bonate, washing it, and then treating it with dilute hydro- 

 chloric acid, neutralizing the acid with ammonia, and 

 adding ammonic oxalate. 



C. MISCELLANEOUS DETERMINATIONS. 



a. Sulphur. — A part of this is volatilized during the 

 process of incineration. In order, therefore, to determine 

 the total amount in the plant, treat 4-5 grms. of the dry 

 substance with fused potassic hydrate and nitrate (§ 92). 



b. Sulphuric acid, already formed in the plant. — A 



few cultivated plants contain more than mere traces of 

 this acid. To detemiine it, and also the chlorine^ if it is 

 desired, prepare an extract of the plant by water contain- 

 ing ^ I20 of nitric acid. 



Draw out one end of a glass tube, about 60 cm. long 

 and 1-1^ 1 2 cm. in diameter, in such a manner that a rubber 

 tube and clamp can be attached, after the fashion of a 

 Mohr's burette. Close the throat of the tube, where it 

 begins to taper into the smaller tube, with a plug of cot- 

 ton that has been previously boiled in the acidulated 

 water, such as is to be used for the extraction. Put 8-10 

 grms. of the dried substance in the tube, fill the latter 

 with the acidified water, and let the two remain in contact 

 several hours ; then open the clamp, let some of the water 

 run off, add fresh acidified water, and repeat the operation 

 until the extract gives at the most the merest opalescence 

 with argentic nitrate. 



