152 TlMEHRI. 
Mean melting point = 186 - 69 degs. c. 
Dulcite 187-26 degs., 187-17 degs., 187-54 degs. 
Mean melting point = 187-32 degs. c. 
The first three determinations of melting point were made with 
laurite that had been simply recrystallised from water until judged 
to be pure ; but the fourth was made on a specimen that had been sub- 
mitted to such treatment as would remove, or at any rate alter, any 
impurity that might have eluded the ordinary method of purification. 
The treatment was as follows : — a portion of laurite already appar- 
ently pure was re-crystallized from hot 10 per cent, caustic soda solution, 
collected and re-crystallised from 20 per cent, sulphuric acid (20 parts 
oil of vitriol 80 parts water), collected, pressed, washed with alcohol, 
dissolved in water and converted into lead compound with ammoniacal 
acetate of lead. The lead compound was well washed with boiling 
water, suspended in water decomposed by sulphuretted hydrogen, and 
the solution filtered. The solution was evaporated to dryness and the 
residue crystallised from rectified spirit. The crystalline form of this 
highly refined product was now found to be exactly the same as before 
the purification and the melting point being 186.60 degrees closely 
approximated to the other determinations. It is therefore considered 
that the result of this experiment fairly proves that laurite is a distinct 
substance and is not merely dulcite with its crystalline form modified 
by some impurity nor mannite with the melting point raised by a 
similar cause. 
The specific gravity of laurite and also of mannite and dulcite were 
determined by weighing the substances in sulphuric ether at the or- 
dinary temperature. No mention appears to be made of the specific 
gravity of mannite in the reference books ; but Gmelin's Hand-book of 
Chemistry states, apparently on the authority of Eichler, that nielam- 
pyrite (synonym for dulcite) has a specific gravity of 1.446 at 15 degs. 
c. In some specific gravity determinations of solid organic bodies 
that have been recently published (Jou?'n. Ckevi. Soc. Abstracts, 1870, 
p. 610) A. Schroder gives the specific gravity of mannite as 1,489. 
However, careful determinations gave the following results : — 
Mannite Laurite Dulcite 
Temp. c. Sp. Or. Temp. c. Sp, Gr. Temp, c Sp. Gr 
26-0 degs. 1-488 26-5 degs. 1-503 26-0 degs. 1-500. 
260 „ 1-188 26-8 „ 1-509 26-7 „ 1-505. 
A 50 gramme Uegnauld's specific gravity bottle was used and the 
