AND TlIK ACTINIC CONSTITUTION OP TIIK ,\TM( »SI'l ll^UIO. 3 



Jill easily measurable, (■lu^inical |ilicii(piiieiinii, wliicli could l)e tin! result nj' ii<> aelinn 

 except tliat of heat, ('an we <;() au)' I'artlier iii our (leuiaiids and rtM^iiic that it 

 should not be exothermic in any degi'ee ? M. lierthelot does not think so, and be- 

 lieves that the addition of enei'gy resulting from the absorption of calorific, lumi- 

 nous, or chemical radiation would not be sufficient to [iroducc a chemical phenomenon 

 which, while going on, would not give rise to a small .amount of heat. I do not 

 very well see why a calorific absorption of solar I'.adijitioii might not compensate 

 for .some heat of cond)ination, and even permit a slightly endothermic I'eaction to 

 appeal'. I have endeavored to discover .some simple method, which, compl3ing 

 with this programme, could be intei'preted without ambiguity, but I hav(( not 

 succeeded. I have been com|icllcd to content my.self with an old, \w\\ known 

 I'eaction — the oxidation which wt-ak solutions of (jxalic acid uiuhMgo upon exposure 

 to light. 



These solutions are and remain transparent. The oxalic acid in them is ti-;uis- 

 forined into carbonic acid, which disappears by ditfusion, so that tht; oxidation 

 which it has undergone can be easily ascertained by an acidimetric determination- 

 made before and after its exposure to light. The reaction thus [)rodnce(l is faintly 

 exothermic, to be sure, but as only very weak solutions are taken, for it is well not 

 to exceed 2 or 3 grannnes of crystal li/>ed oxalic acid per litre, there is no rea.S(Hi 

 why we should be troid)led about the erroi' which .arises from this f.act. Moreovei", 

 the liberation of heat, which results from combustion, even if it should be perce[>- 

 tible, would rem;iin without effect, foi' oxalic atiid oxidizes only with extreme .slow- 

 ness under the intluence of heat .-done. 



J^Jxp. — 10 c. c. of ;i solution of o.\;dic acid, titrating 10 c. c. of lime-watei- pci- liti'e, 



was heated on a water bath to nearly 95", in a ilask of 125 c. c. 



After heating 4 honi's, the titre is 18.5 c. c. Lo.ss 2.G per cent. 

 y " " " IS.o " " 5.2 " 



Mq). — 10 c. c. of ••inothei' solution, titrating lO.G c. c. of lime-water per litre, was 



heated an hour and ;i half to 1 15°. 



The titre falls only to M).2 c. c. and 1(1.1 c. c. 

 During the days of gi'eatest he.at, the tempeiiiture hardly exceeds 50" in the 

 shallow vessels, in which the li(piid is exposed to the sun. It m;iy, therefore, be 

 assumed that neither tlu^ so|;u- heat nor the heat produced by combustion liave any 

 perceptible elfect upon the transfoi'mation of the oxalic acid, which m;iy, <>n 1in(! 

 days, reach or even exceed 50 pel' cent of the acid contain(Hl in the st)lution. 



As the calorific rays have h.anlly any power, it wcmld be desirable to eliminate 

 the action of the luminous rays also, but the chemical radi;itions are so closely in- 

 termingled with the latter that it is difficult to separate them. Let us lu- content. 



