208 ANNUAL OF SCIENTIFIC DISCOVERY. 



dial plate, on the axis of which is placed a pointer and pinion. To the end 

 of the other tube is fixed a toothed rack, which communicates motion to the 

 pinion. Hence, when the temperature varies, the tubes will vary in their 

 expansion and contraction, and the pointer will indicate on the dial the 

 temperature for the time being to which the thermometric apparatus has 

 been subjected. 



The advantage of the instrument consists in its capability of indicating 

 degrees of heat beyond the limits of the ordinary mercury thermometer, its 

 power being only limited by a temperature so high as to cause the metals of 

 which it is composed to lose their rigidity. Its advantage also consists in 

 the heat acting directly upon the sensitive part of the instrument, no inter- 

 vening substance such as glass being made use of, as in the case of the mer- 

 cury thermometer, unfitting that instrument to be applied to high tempe- 

 rature from the danger of its being destroyed by reason of the glass tube 

 flying to pieces. 



These pyrometers have been in use for some months past at several iron- 

 works in the north of England, and we understand have been very highly 

 approved of. 



ON THE EFFECTS OF HEAT ON THE COLOR OF DISSOLVED SALTS. 



Dr. Gladstone, in a paper before the British Association, Dublin, stated 

 that if a colored salt be dissolved in water, heating the solution does not 

 usually affect the color of it. In not a few cases, however, the color is ren- 

 dered more intense, and altered somewhat in its character. Among the ex- 

 amples mentioned were ferricyanide of potassium, mcconate of iron, 

 chloride and bromide of palladium. In other cases, heating the solution 

 produces apparently a total change of color; for instance, chloride of copper 

 passes when heated from blue to green ; chloride of nickel from a bluish to a 

 yellowish green ; sulphocyanide of cobalt, or chloride of cobalt dissolved in 

 aqueous alcohol, from a pale red to a deep bluish purple. In all these in- 

 stances hetit causes the absorption of a larger quantity of rays by the solu- 

 tion ; but this appears to depend sometimes upon some purely physical 

 cause, at other times upon some chemical change. With ferricyanide of 

 potassium, and similar salts, a certain thickness of the heated solution pro- 

 duces precisely the same effect on the spectrum as an increased thickness of 

 the same solution when cold. With chloride of copper, and similar salts, 

 the somewhat dilute solution when heated, produces the same effect on the 

 spectrum as the same solution when concentrated and cold, these salts 

 being all of that character which is altered in color by the addition of water. 



ON THE SOLIDIFICATION OF FLUIDS. 



In a paper on the above subject, submitted to the British Association, 

 Dublin, hy Prof. Hennessy, the views put forward were deduced from some 

 propositions in the dynamical theory of heat contained in the writings of 

 Prof. W. Thomson and Prof. Clausius. The general result arrived at re- 

 garding the influence of pressure on a fluid so circumstanced as to lose no 



