400 



DETERMINATION OF ALKALIES IN SILICATES. 



already referred to, which is made to incline a few degrees 

 downward by turning the plate of iron that supports it. c is a 

 chimney of sheet-iron, eight to nine cm. long, ten cm. high, the 



width at the bottom being about 

 four cm. at one end and about 

 three cm. at the other end. It 

 is made with the sides straight 

 for about four cm., then inclines 

 toward the top so as to leave the 

 width of the opening at the top 

 about one cm. A piece is cut out 

 of the front of the chimney of the 

 width of the diameter of the hole 

 in the iron support, and about 

 four cm. in length, being semi- 

 circular at the top, fitting over, 

 the platinum crucible. Just above 

 this part of the chimney is riv- 

 eted a piece of sheet-iron in the 

 form of a flattened hook n, which 

 holds the chimney in place by 

 being slipped over the top of the crucible support; it serves as 

 a protection to the crucible against the cooling of the currents 

 of air. / is the burner, which has been described in the article 

 on flame-heat. The upper opening of it is a slit from one and 

 a half to two mm. in width and from three and a fourth to four 

 and a half cm. long, and when used is brought within about 

 two cm. of the lowest point of the crucible, the end of the 

 flame just playing around the lower end of the crucible; the 

 gas enters the lower part of the burner by two small holes 

 of one sixteenth of an inch, furnishing at one inch pressure 

 about five and a half cubic feet of gas per hour; the precaution 

 must be observed, already referred to, in heating the crucible 

 at first gently above the mixture. It is surprising to see the 

 effect produced by this simple burner as here used ; eight 

 grammes of precipitated carbonate of lime can be decomposed 

 to within two or three per cent, in one hour, and when mixed 

 with silica or a silicate in a very much shorter space of time, 

 although in my analysis I employ one hour, as it requires 

 no attention after the operation is once started. This form 





