28 



CLARKE 



Compound. 



Methyl acetate 



Ethyl formate 



Methyl propionate... 



Ethyl acetate , 



Propyl formate , 



Methyl isobutyrate . 



Isobutyl formate , 



Allyl formate 



Dimethyl carbonate 

 Diethyl carbonate.., 



Ethyl nitrate , 



Ethyl nitrite 



Isobuty] nitrite 



Amyl nitrite 



Nitromethane , 



Nitroethane 



Heat of Combustion, Thomsen. 



HjO Liquid. 



399240 

 400060 

 553950 

 546570 

 55S800 

 716940 

 719900 

 527900 

 357570 

 674100 



324040 

 334210 

 647660 

 812640 

 180900 

 337940 



H.O Gas. 



Calculated 'Percentage Thomsen' s 

 ^^"^"'^"'^•' Difference. \ Variation. 



367971 

 368791 

 512258 

 504878 

 517108 

 664825 

 667785 

 496631 

 326301 

 621985 



297982 

 308152 

 600756 



755313 

 165265 



365092 

 365092 

 509749 

 509749 

 509749 

 654407 

 654407 

 489083 

 316871 

 606188 



299649 

 320315 

 609632 

 754290 

 175656 

 320315 



—0.79 

 — I.OI 



—0.49 

 +0.96 

 —1.44 



—1-59 

 — 2.04 



—1-54 

 —2.98 

 — 2.60 



+0.56 

 +3-94 

 + 1-47 

 — 0.13 

 +6.28 

 +2.70 



0.52 

 1.04 

 0.46 

 0.76 

 0.48 



0.78 

 0.47 

 0.75 

 0.22 



0.31 

 0.14 

 0.67 



0.43 

 0.85 

 0.50 



In the foregoing computation the heats of combustion of the 

 compounds named have been assumed to be multiples of the 

 fundamental constant by quantities derived from a definite gen- 

 eral formula. The average variation between observation and 

 theory, in 112 cases, is 1.09 per cent,, and the variations are 

 distributed as follow^s : 



Variation over 2 percent i6 compounds. 



Between i and 2 percent 39 compounds. 



Under i percent 57 compounds. 



If we reject, as defective, the observations giving variations 

 above 2 percent, the average variation in the remaining 96 

 instances is 0.84 percent. Is this amount excessive, or is it 

 satisfactory? To answer this question we must examine the 

 sources of uncertainty in the measurements. They may be 

 summarized thus : 



First. — Impurity in the material studied. This error cannot 

 be absolutely avoided, but in Thomsen's work it is doubtless very 

 small. In some cases impurities were recognized, and correc- 

 tions were applied for them. 



Second. — Incomplete combustion. Error probably insignifi- 

 cant. 



Third. — Thomsen's data, as cited, all relate to gases at con- 

 stant pressure. They should be reduced to constant volume. 

 The correction would lower the results of measurement by small 



