4 o 4 



Progress in Science. 



[July, 



and long-continued alterations of temperature, or by other agencies, this 

 molecular change of silver may possibly throw some light upon the similar 

 change observed in the case of iron. 



A very convenient arrangement for heating crucibles by gas is described by 

 Professor J. Lawrence Smith, in Crookes's " Select Methods in Chemical 

 Analysis," p. 408. It has been found of the greatest use in the analysis 

 of silicates, but it will be equally useful in other branches of analysis where 

 fusions at a high temperature are required. The figure here given illustrates 

 the stand, burner, crucible, &c, and is about one-sixth the natural size, h is 

 the stand with its rod, g. d is a brass clamp, with two holes at right angle to 

 each other ; having two binding screws, it slides on the rod, g ; the second 

 hole is for a round arm attached to b, the binding-screw, e, fixing it in 

 any position, b is a plate of cast-iron, 5 to 6 m.m. thick, 10 to 11 centims. 

 long, and 4^ centims. broad, having a hole in its centre large enough to admit 

 the crucible to within about 15 m.m. of the cover without binding, a is 

 the crucible, which is made to incline a few degrees downwards by turning the 

 plate of iron that supports it. c is a chimney of sheet-iron, 8 to g centims. 

 long, 10 centims. high, the width at the bottom being about 4 centims. at one 

 end, and about 3 centims. at the other end. It is made with the sides 

 straight for about 4 centims., then inclines towards the top, so as to leave the 

 width of the opening at the top about 1 centim. 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 4 centims. in length, being semicircular at the 

 top, fitting over the platinum crucible. Just above this part of the chimney is 

 rivetted 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 



Fig. g. 



serves as a protection to the crucible against 

 the cooling effects of the currents of air. f 

 is the burner, the upper opening of which 

 is a slit from i\ to 2 m.m. in width, and 

 from 3 to 4 centims. long, and when used 

 is brought within about 2 centims. 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 

 i-i6th of an inch, furnishing at i-inch pres- 

 sure about 5^ cubic feet of gas per hour. 

 It is surprising to see the effect produced 

 by this simple burner as here used ; 8 grms. 

 of precipitated carbonate of lime can be 

 decomposed to within 2 or 3 per cent in 

 one hour, and when mixed with silica or a 

 silicate, in a very much shorter space 

 of time. A method invented by Thiercelin 

 has been successfully used in extracting 

 iodine from crude Chili saltpetre. The 

 mother-liquors resulting from the manufac- 

 ture of saltpetre are treated with a mixture 

 of sulphurous acid and sulphite of soda, and 

 the iodine will be precipitated as a black 

 powder. This is placed in earthen jars, on 

 the bottom of which are layers of quartz- 

 sand, fine at the top and coarse at the bottom; from these jars it is removed 

 by earthen spoons lined with gypsum, and the greater part of the water 

 is thus separated. It is further purified by sublimation, but is often sold 

 before undergoing the last-named process. The amount of iodine thus 

 reclaimed from Chili saltpetre already amounts to 30,000 pounds per annum. 



Up to a few years ago indigo was considered to be insoluble in almost 

 all agents which did not decompose it. Now several agents are known 



