OXlMlD0SULl>li(_)XATES Ol.' SULPIIAZOTATES. p,] 



powdered nentral salt int«» the alkaline one is not vei'v apparent to the 

 eye. Yet the potas^inm liych-oxide is withrh-awn by the powdered 

 salt rapidly from the solution, which consequentlv loses all its caus- 

 ticity to the toniiMie. When used concentrated the alkali causes, as 

 Fremv noted, a heatinu' up. wliile when it is dilute it causes, we find, 

 a fall of temperature amountinu' to about three degcees, due no doubt 

 not to dissolution of s;iJt so much as to liquefaction of three-fourths of 

 the water of crystallisation of the neutral salt transformed. 



Claus denied altog-ether that the neutral salt could be converted 

 into the alkaline salt, and Raschig found it necessary for success to 

 modify Fremy's process. The latter uses twice the calculated quantity 

 of potassium hydroxide and in concentrated solution, heats to boiling, 

 and crystallises the salt by cooling. The salt is purified by recrystal- 

 lisation from water. Weak alkaline solutions of the neutral salt 

 did indeed yield him crystals of the alkaline salt, but in order to 

 do so had to be left to stand for some weeks. According to our 

 experience, however, any excess of alkali is unnecessary and best 

 avoided, as then the alkaline salt is at once obtained pure. Neither 

 need the solution of the alkali be concentrated ; nor the mixture be 

 heated to boiling ; nc^r time be given, more than is usual for crystal- 

 lising out salts. When crystallisation happens to be slow in setting 

 in, a particle of the solid salt, previously obtained, at once determines 

 it when dropped into the solution. 



Alkaline jiotnssium sodiwn oxùnidostdph ouates.- — There is some dif- 

 ficulty in preparing potassium-sodium salts having a basicity as great 

 as that of the more alkaline sodium or potassium salt, but several less 

 alkaline can be obtained liy mixing in solution the neutral potassium 

 salt with sodium hydroxide, (^r the neutral sodium salt with potassium 

 hydroxide, and either evaporating or adding alcoliol. 



AJhtlinr hariinu, ><trn)ititnii, and lead mils. — Addition of barium 



