Intelligence and Miscellaneous Articles. 395 



It is well known what difficulties accompany the separation of the 

 acids of arsenic and of antimony, as likewise tliat of the peroxide of 

 tin, from bases. In general these metallic acids are separated from 

 the solutions of most of their salts in hydrochloric acid, or to which 

 hydrochloric acid has been added, by sulphuretted hydrogen, as 

 sulphurets, and the base in the filtered liquid determined in the state 

 of chloride. If the latter happens to be one which is easily decom- 

 posed at an elevated temperature, and not volatile or only so at a 

 very high temperature, the liquid, which is frequently very con- 

 siderable in quantity, has to be evaporated to dryness, and the resi- 

 due ignited more or less strongly. Every one accustomed to ana- 

 lytical investigations must be sufficiently well acquainted with the 

 inconveniences which accompany tlie evaporation of large quantities 

 of liquids containing small amounts of alkaline salts, which have to 

 be determined {juantitatively. 



The difficulties attending such an investigation become greater 

 when the salt of the metallic acid is not at all, or very sparingly, 

 soluble in water and in hydrochloric acid, or one which is easily 

 decomposed. Now this is frequently the case with a salt of this 

 class when it has been heated to redness, which is requisite in deter- 

 mining the amount of water directly. 



All these difficulties may in many cases be avoided by the use of 

 chloride of ammonium. Suppose we have a salt of one of these 

 metallic acids with an alkaline base to examine, it is only requisite 

 to mix it, after having ignited and weighed it in the finely-pulverized 

 state, with from five to eight times the quantity of pure powdered 

 chloride of ammonium, and to heat the mixture in a small porcelain 

 crucible which may be covered with a concave platinum lid, over an 

 Argand lamp until the whole of the chloride of ammonium is vola- 

 tilized. The alkali is left behind in the state of chloride, the quan- 

 tity of which may be very accurately determined. So long as chlo- 

 ride of ammonium is volatilized, the temperature is so low that none 

 of the alkaline chloride can escape. As soon as the ammoniacal 

 salt is driven off, the temperature is moderated, so that the residue 

 in the porcelain crucible does not fuse. After weighing, it is mixed 

 with a fresh quantity of chloride of ammonium and again heated, in 

 order to see whether the weight of the residue remains constant or 

 is diminished, in which latter case the treatment with chloride of 

 ammonium must be repeated. Sometimes, owing to the access of 

 air, the platinum lid is coated with a film of the metallic acid, espe- 

 cially with peroxide of tin when stannates are examined. In this 

 case, the lid, in the subsequent Ignition, is covered with a little of 

 the ammoniacal salt. 



I will here describe some experiments which have been made by 

 M. Weber : — 0"609 grm. of ignited arseniate of soda, 2NaO + AsO*, 

 afforded, after being once treated with five times the amount of 

 chloride of ammonium, 0'455 grin, chloride of sodium. The weight 

 remained the same after repeating the treatment with chloride of 

 ammonium. The quantity of chloride of sodium corresponds to 35"46 

 per cent, soda in the salt; the theoretical quantity is 35'18. 



