Chemistry and Physics. 69 
Since the molecule _ one wisi tak weighs 100, it follows that 
425 units of heat, ound numbers, are abs orbed for every unit 
of weight of ied ale yr rded as tare calcite) burned in a lime 
iln, Favre and Assipony found for the same constant the value 
308 units which is } too small. A comparison is made in this 
paper of the heat of iecustion of the anhydrous carbonates and 
pen ates of the same metal, oreeaed to the general reac- 
s R’+0,+.C0 and R" +0,+50,, from which it appears 
tat the alfferbuce i is far from constant. In most cases the heat of 
formation of the sulphate is Spe than that of the carbonate, 
the difference varying from 22,620 heat units in the case of the 
potassium salts to 3430 units in the case of the silver salts; but 
in the case of the salts of cadmium and manganese she conditions 
that SO, and CO, stand in different relations to the molecules of 
the salts, in which these redicads are supposed to exist as actual 
atomic groups 
(2) In his previous investigations on the heat of formation of 
the oxides and acids of nitrogen, Thomsen had left undetermined 
the heat of Sonatas of NO, which enters as a radical into so 
many of this class of compounds, The determination of this im- 
portant vig Rae This the construction of a special aja and 
for this, as well as for other reasons, has been delayed. The result 
now r stad “differs greatly from that obtained by Berthelot, pe 
if aloes, will require a material correction of some of the most 
import ant thermo-chemical data. peoeeting to Berthelot, N+ 0 
= — 43,300 units, while ips o Thomsen this value should 
be ~36,395 units. Thom t elaton ‘that there is a large error in 
ha gen. How great a change the correction thus introduced makes 
in some a partant values calculated from the old data, the follow- 
ing table shows: 
Berthelot. Thomsen. 
N.+0, —48,660 — 33,650 
N,+0;+Aq ws 800 +180 
For a large number of other thermo-chemical data corrected for 
the ed fundamental value of N +O, we must refer is loc. cit., 
page 2 5. Pi; Og FR 
7. a New Standard of Light—Mr, Louis Se HWENDLER 
presents the advantage of using the incandescence of platinum by 
Means of a constant electric current for a standard of light. In 
foot-notes he states that this is not a new idea and refers to Dr. 
