70 Inteiligence and Miscellaneous Articles. 



stances with an excess of bichromate of potash, pouring water over 

 the mixture in a platinum or porcelain crucible, and then drying it, 

 lirst in the water-bath and afterwards in the air-bath, at 392° Fahr. 

 In manj' cases the mixture may be heated almost to redness over 

 the tlame of a lamp. 



The intermixture of bichromate of potash is a source of oxygen, 

 which readily furnishes that substance to the oxidizable body, with- 

 out, however, in any way altering the weight. Consequently if the 

 weight of the substance employed, and of the bichromate of potash 

 added to it be known, the loss, if no volatile body be present, gives 

 only the quantity of the water contained in it, and volatilized from 

 the substance under investigation. It is a matter of course that this 

 substance should contain neither organic compounds nor ammo- 

 niacal salts. I'he addition of bichromate of potash is not always 

 advisable, but in many cases the neutral salt must be employed, as 

 in many salts the acid will have a decomposing action upon the 

 chromic acid, giving rise to an evolution of oxygen or chlorine, 

 and thus a higher amount of water will be obtained. This will 

 occur, for instance, with all protosalts of iron containing sulphuric acid 

 or chlorine ; with these the neutral chromate of potash must always 

 be employed, when, if the heat be not raised to redness, no decom- 

 position of the chromic acid will take place. The chromate employed 

 must be perfectly dry and free from all organic matter. 



To obtain it in this state, the commercial salt is to be purified by 

 crystallization, and the crystals obtained fused at a gentle heat 

 (below redness) in a platinum or porcelain crucible. On cooling, 

 the mass solidities at first in a crystalline form, and afterwards falls 

 into a coarse powder, which may be employed M'ithout further pre- 

 paration, and should be weighed while still warm. The neutral 

 chromate of potash is dried in a covered crucible and weighed Vhilst 

 warm. — Liebig's Annalen, May 1855, vol. xciv. p. 216. 



ON THE DETERMINATION OF LIME. BY H. VOHL. 



Lime is usually determined either as carbonate or sulphate. A 

 method which furnishes very exact results consists in precipitating 

 the lime in the form of oxalate, washing the precipitate by decanta- 

 tion, and then treating it in the apparatus of Will and Fresenius 

 with bichromate of potash and sulphuric acid. If a few particles 

 float upon the surface during the decantations, they may be got rid 

 of by the addition of a few drops of aether. The sulphuric acid sets 

 free the oxalic acid of the lime-salt, which is then oxidized by the 

 chromic acid, forming carbonic acid, which is evolved. From this 

 loss the amount of lime is calculated in accordance with the follow- 

 ing formula : — 



3(CaO, C9 03) + KO, 2(CrOs) -|- 7(S03) 



= 3(CaO, S03) -I- KO, SO' -|- Cr^ O' -f 3(80') -|- 6(C0-), 

 or for 84396 of lime, 132*000 of carbonic acid will be evolved. 



