226 $'TEMPERATURES OF MAXIMUM DENSITY.—MACGREGOR, 
Art. VIL—Note oN TempeRaTURES of Maximum DeEnstry. 
By Pror. J. G. MacGregor. 
(Read May.J 
KoHLRAuscH* has investigated the expansion of Vulcanite 
(Hartgummi, Kammumasse,) and found that between 16° and 
35° C the true linear coefficient of expansion (e) at the tempera 
ture ¢ is given by the formula: 
==6 —-§ 
€ 2/618 10) TORUS gt 
If the formula hold beyond the experimental limits, it follows 
that e must have the value 0, when 
= a= 81 O10 
For higher values of ¢, ¢ will be positive; for lower values 
it will be negative. At this temperature, therefore, Vulcanite 
must have minimum volume or maximum density, if the above 
formula holds. The probability that the fermula deduced from 
experiments between +16° and +35° should be true for —80 ° 
is not Great, but it may, nevertheless, be worthy of notice that it 
indicates Vuleanite as being perhaps one of those peculiar sub= 
stances having temperatures of maximum or minimum density, 

The fellowing substances have also laws of expansion within 
the limits of experiment, which indicate temperatures of maxi- 
muin or minimum density beyond these limits: 
Maxie Dendy, | Miniea neleg 
Dianiond#....... ert anes og STO OCs Se ee ae eee : 
Copper Oxidet 010s... 25 reaeeeye = 4.3 Sees 
Bimierald-).; S.gk kat. Pee sos ee ES ree, 
(0) 
fodide of Silvert (crystal)........ ...%2 viggiaass  —=lo7 
Do. (GHSE) tinea bloat Gace 6 Pare ~= 59.3 
Do. (compressed precipitate)........ —= 45.4 


* Pogo, Ann. Phys. Chem.—cxlix (1873), p: 577. 
+ Fizeau, Comp. Rend. Ixviii., p. 1125 (Pogg. Ann. Phys. Chem., exxxviii. (1869), p. 26. 
_ }Fizeau, Comp. Rend., Ixiv. (1867), pp: 314 and 771—(Pogg. Ann. Phys. Chem., exxxti (1867) #- 
B92.) 
