380 
Scientific Intelligence. 
[Dec. 
subject: the writer does not give the specific gravities of the ingredients of the com- 
pound which he has used in his computations, so that we are at a loss to judge how 
far |iis results are likely to he correct. It is notorious, how little agreement there 
is in this determination as made by different experimenters, and were we to take 
the limits of some of the bodies be lias included in his table, we might bring out at 
pleasure a result higher or lower than the experimental one. The subject is a very 
interesting one, particularly as connected with the prime equivalents or combining 
weights of bodies, and we think promises to reward any one who shall devote his 
time and attention to it. 
3. Expansion of Air, 
In the latter part of the preceding paper, the author takes notice of another error 
in a work of authority, (Brande’s Chemistry.) He might have added lire’s Chemi- 
cal Dictionary, and possibly many other works. Ure’s error is the more extraordi- 
nary, as he professes to give his table instead of one which will be found in Thom* 
son’s Chemistry, 6th edition, vol. 1, p. 29 which he represents as useless. Now 
the real state of the case is, that his own table being erroneous, is worse than useless, 
while Thomson's, though not so convenient in use as it might be, is strictly correct. 
The error in Brande was pointed out some years ago in the Annals of Philosophy 
by a Mr. Biggs. The error is this : — Air has been found to expand from a volume 
of 1 to 1,375, when heated from 32° to 212°, and again from 1,375 to 1,75 when 
further heated to 392° increasing by, 375 of what its volume at 32° would he for 
each increase of temperature measured by 180° Fall. It is therefore concluded that 
for every 1° it expands ,002083 of what the volume would he at 32°. The words in 
Italics being lost siglit of, occasions the error. Thus Ure and Braude assume 
that it expands ,002083 of the volume at 60° which is evidently at variance with 
the above law. 
The rule for reducing the volume of air at a given temperature to what 
it would be at another, is as follows. Multiply the given volume by 448, 
increased by the resulting or new temperature, and divide by 418, increased by 
the given temperature, the quotient is the resulting volume. Or in symbols, 
440XT 
448 + T. 
The table in Thomson’s Chemistry before referred to, will furnish the proportionate 
volumes at different temperatures, from which, by a simple statement of the rule of 
three, the resulting volume may be found. 
4. On the use of Plumbago (Graphite,) instead of Oil , in Chronometers. 
In vol.xvi. of the Transactions of the Society for the Encouragement of Arts, Ma- 
nufactures, and Commerce, appears an account by Mr. L. Herbert, of his method of 
applying plumbago to the pivots of the works in chronometers in lieu of oil, to 
which it is known there are many serious objections. Mr. Herbert obtained the 
gold medal for his discovery. His method of applying it, is as follows : Having 
obtained some of the finest plumbago or graphite, (as it should rather be called) 
from Mr. Langdon, the celebrated manufacturer of pencils, be pounded it in a metal 
mortar till it became so fine as to feel greasy to the touch. It was then diffused in 
water. Part sunk down and part swam upon the top in a kind of film. This was 
taken off carefully with the blade of a knife and set by. The same operation 
was performed with another portion, the film being set by for use, and the ope- 
ration continually repeated until a sufficiency was obtained. The fine powder col- 
lected, is now to be bruised with the back of a spoon, and again diffused in water ; if 
pure, there will he now no sediment, the whole floating on the surface. The wash- 
ing is to he continued till this result is obtained, and then you may be sure the gra- 
phite is pure. Some pure alcohol is now to be poured into a glass — the pivot dipped 
in it, and then in the powdered graphite. Then put some of the powder into the 
pivot holes by rubbing them with a little taken on the finger till even with the plate, 
and the hole appears filled. Now insert the pivot, and turn it with the hand several 
times. Repeat the whole operation two or three times. In the case of a clock, 
there was difficulty in making it adhere to the jewelled pallets of the escapement, 
but this was obviated by applying it to the friction planes of the teeth of the swing 
wheel. 
A sidereal clock being thus treated in January 1816, had been cleaned three times 
without the plumbago (graphite) being renovated. The friction surfaces were merely 
wiped with a fine piece of muslin, and in 1827, it was found to go as well as ever. 
