206 DETERMINATION OF ALKALIES IN MINERALS. 



21. It will be seen that thus far the operations have been 

 carried on in the capsule in which the fusion was dissolved. 

 The contents of the capsule are now thrown on a filter; but 

 before doing this it is well to pour on a little of the solution 

 of the carbonate of ammonia, and see if the clear part of the 

 liquid be rendered turbid; in other words, ascertain if sufficient 

 carbonate of ammonia had been originally added. 



22. The solution that passes through the filter contains much 

 sal ammoniac, the alkalies of the mineral, and a little lime. If 

 magnesia be one of the ingredients of the silicate examined, 

 some of this is also present; and in still rarer instances some 

 of the earths soluble in carbonate of ammonia. This latter 

 complicates in no degree the remaining steps in the analysis. 

 It is best to let the filtrate pass into a glass flask. The washings 

 of the filter are collected in another vessel and concentrated to- 

 a small bulk, added to the first filtrate, and the whole boiled 

 for some time to drive off the carbonate of ammonia.* When 

 no great haste is required in the matter the whole filtrate (first 

 portions as well as the washings) are collected in a beaker and 

 concentrated over a sand-bath. What remains now to do is to 

 separate from the alkalies the substances above alluded to. I 

 commence by getting rid of the sal ammoniac, and this brings 

 me to the third part of this paper. 



III. The removal of the Sal Ammoniac unavoidably accu- 

 mulated IN THE PROCESS OF ANALYSIS. 



23. This is probably one of the greatest annoyances to the 

 analyst in his examination of minerals: first, from the manner 

 in which the salt creeps up the sides of the vessel in which 

 the evaporation to dryness is carried on; and secondly, from 

 the great difficulty of preventing loss of the chlorides of the 

 fixed alkalies during the volatilization of the sal ammoniac. 

 A better idea is formed of this by an experiment with a known 

 quantity of the alkalies mixed with sal ammoniac. An array 

 of the precautions requisite to be taken can be seen in Eose's 

 last edition (German), pages 6 and 7. Owing to these difficul- 

 ties, which my experience has often led me to contend with, 



* What remains in the filter is silica, alumina, fluoride of calcium, oxide 



