220 Scientific Intelligence. 



generation of heat, or at least the amount should be uncertain. 

 Finally, if all the acid passed over to the soda, the amount of 

 heat set free should be 1-12. The amount actually observed 

 equalled 1*07, which as the probable error is ±-04, evidently sen- 

 sibly equals 1-12. The very small difference of -05 is also ex- 

 plained by the purely physical action exercised by ammonia on a 

 solution of chloride of sodium. In fact a mixture of the same 

 quantities of ammonia water and chloride of sodium absorbs -05 

 units of heat. Similar effects are also obtained by replacing the 

 chloride by the nitrate or sulphate, or by using potash instead of 

 soda, Not only can ammonia be replaced by soluble bases such 

 as potash or soda, but even by those which are insoluble, such as 

 lime. According to Berthollet there should be a division at first, 

 then a precipitation of the lime, and so on until it was wholly 

 separated. But this effect is not produced, the lime is not pre- 

 cipitated but dissolved in the chloride of ammonium. To deter- 

 mine the real nature of the reaction a certain amount of lime was 

 precipitated from the chloride by soda; 1-18 units of heat were 

 thus absorbed. It was then dissolved by chloride of 



5 of heat 

 the solution 



heat were disengaged. But in the latter opera- 

 of the hydrate of lime by the ammonia should 

 ts of heat; and the redissolving of the lime 



should give out 1-10, or in all 2*20, which agrees closely with 2"24, 

 the observed amount. Again, the total heat set free, — .l-18+2"24 

 = 1-06 is very nearly equal to VOI, the amount set free in the 

 previous experiment by the direct action of the soda on the chlo- 

 " " . -^ ^ ^ ^ YtYove that the double 



t the cause of the pbe- 

 i ; while they are completely explained by the complete 

 ubstitution of the lime, a nearly insoluble base, by the ammonia, 

 I soluble base. We see therefore that this substitution may take 

 >lace contrary to the laws of Berthollet.— ^ww. Chim. et Phys., 



Pyrheliometer.—M.. A. Cbova has measured the cal- 



orific intensity of the solar radiation and its absorption by the 

 atmosphere of the earth. With the pyrheliometer of Pouillet it 

 appeared that the indications varied with the method of preparing 

 the surface. If the silvered chamber containing the water is sim- 

 ply covered with one or more coatings of lampblack, a portion of 

 the heat after passing through the coating is reflected by the 

 metal and thence passes out through the lampblack which is 



•a. layer ui puixiuum DiacK. A large cnermomeier naviug a "u\" 

 40 mm. in diameter and a tube 300 mm. long replaces the ordi- 

 nary silvered box. The bulb is covered with silver, copper, plati- 

 num, and finally with a thin coating of lampblack. The tube 



