928 Natural- Philosophical Collections. 
swer ; but the important point of being able to make artificial ultramarine, by the 
action of clay and sulphate of soda, was distinctly ascertained. It is also remark- 
ed that sulphate of soda, prepared without any excess of acid, may be converted 
into sulphuret, and become reddish brown by the sole influence of heat ; but that 
when excess of acid is present, this decomposition cannot take place, and no ul- 
tramarine can be formed.— Annales de Chimie, x1. 439. 
On the Formation of Acids in Vegetables, by M. Vauquelin.—I have thought 
that, in a great number of cases, the developement of acidsin vegetables was prin- 
cipally occasioned by the presence of alkalies. We find, in fact, the acids al- 
most always neutralized altogether, or in part, by various alkalies, as lime, po- 
tash, soda, magnesia, and sometimes by vegeto-alkalies; and I do not know 
that the latter have ever been found in a free state in the vegetable kingdom. 
The alkali which plays the greatest part in this respect is certainly lime, for 
it is most generally diffused, is most abundant at the surface of the earth, and 
powerfully attracts acids. It does not, certainly, enter into the organic kingdom 
in the state of lime, but as a carbonate, which, without exerting any deleterious 
action on vegetables, still retains sufficient alkaline force to determine the forma- 
tion of acids, and particularly the oxalic, which it prefers to all others. 
We may thus, as I have said elsewhere, explain the effect of calcareous ma- 
nures on vegetables. Immediately after its introduction into the organs of plants, 
the carbonate of lime determines the developement of an acid which decomposes 
it, and sets its carbonic acid at liberty, which, by means of light, is turned to 
account in the vegetable kingdom. From hence, it may be concluded that cal- 
carous manures fill two important functions ; namely, the division of the soil, 
and the nutrition of the plants.— Ann. de Chimie, xli. 59. 
Results of Mr. Rennie’s experiments on the friction and abrasion of the sur- 
faces of Solids.—The following are the results of a series of very valuable expe- 
riments on friction, made by John Rennie, Esq. 
The table shows the amount of friction (without unguents) of different sub~ 
stances, the insistent weight being 36lbs. and within the limits of abrasion of the 
softest substance. a 
Parts of the 
whole weight. 
Steel on ice, - - < = = - 69.81 
Ice on ice, - - = - - - 36.00 
Hard wood on hard wood, mf - - 2 VET 
Brass on wrought iron, - - - = - 7-38 
Brass on cast iron, - = = - - 7.11 
Brass on steel, - = < = = - 7.20 
Soft steel on soft steel, - = 2 - - 6.85 
Cast iron on steel, - = - ~ - 6.62 — 
Wrought iron on wrought iron, = . - 6.26 
Cast iron on cast iron, - - - - . 6.12 
Hard brass on cast iron, - = - - 6.00 
Cast iron on wrought iron, = is = = 5.87 
Brass on brass, - : - : - 3.70 
Tin on cast iron. + - ~ - - 5.09 
Tin on wrought iron,’ - = = - = 9.03 
Soft steel on wrought iron, - - - -  §.28 
Leather on iron, = = - - - 4.00 
Tin on tin, a = - - es = 3.78 
Granite on granite, - - - 5 c, 3.30 
Yellow deal on yellow deal. - - - - 2.88 
Sand-stone on sand-stone, - - - - 2.79 
Woollen cloth on woollen cloth, - - - 2.30 
These results are collected from the different Tables, but the comparison may be 
made by selecting other values within the limits of abrasion fora minimum, ~ 
i 
