274 

NATURE 

[Aug. 3, 1871 

themselves, as far as I know, have never appeared in an entire 
form, I will crave permission to have them printed as an ap- 
pendix to this address. Lavoisier, it will be seen, addresse~ 
Black as one whom he was accustomed to regard as his 
master, and whose discoveries had produced important revolu- 
tions in science. It may indeed be said with truth tha: La- 
voisier completed the foundation on which the grand structure 
of modern chemistry has since arisen; but Black, Priestley, 
Scheele, and Cavendish were before Lavoisier, and their claims 
to a share in the great work are not inferior to those of the illus- 
trious French chemist. 
Among the questions of general chemistry, few are more inte- 
resting, or have of late attracted more attention, than the relations 
which subsist between the chemical composition, and relractive 
power of bodies for light. Newton, it will be remembered, 
pointed out the distinction between the refractive power of a 
medium and its refractive index, and gave for the former the 
expression Ma—! where mu is the refractive index, and @ the 
da 
density of the refracting medium. Sir J. Herschel. anticipating 
later observations, remarked in 1830 that Newton’s function only 
expresses the intrinsic refractive power on the supposition of 
matter being infinitely divisible, but that if material bodits con- 
sist of a finite number of atoms differing mm weight for different 
substance-, the intrinsic refractive p »wer ot the atoms of any given 
medium will be the product of the above function by the atomic 
weight. The same remark has since been made by Bertholet. 
Later observations have led to an important modification in the 
form of Newton’s function. Beer showed that the experiments 
of Biot and Arago, as well as those of Dulong on the refractive 
power of gases, agree quite as well with a simpler expression as 
with that given by Newton ; and Gladstone and Dale proposed 
in 1863 the formula “—! as expressing more accurately than 
} = P g yi 
any other, the results of their experiments on the refractive 
power of the liquids. The researches of LandoJt and Wiillner 
have fully confirmed the general accuracy ot the new formula. 
An important observation made, about twenty years ayo by 
Delffs, has been the starting point for all subsequent investiga- 
tions on this subject. Delffs remarked that the refractive in- 
dices of the compound ethers increase with the atomic weight, 
and that isomeric ethers have the same refractive indices. The 
later researches of Gladstone and of Landult have, on the whole, 
confirmed these observations, and have shown that the specific 
refractive power depends chieHy on the atomic composition of 
the body, and is little influenced by the mode of yrouping of the 
atoms. These inquiries have gone further, and have led to the 
discovery of the refraction equivalents of the elements. By com- 
paring the rfractive power of compound bodies differing from 
one another by one or more atoms of the same element, Lan- 
dolt succeeded in obtaining numbers which express the refraction 
equivalents of carbon, hydrogen and oxygen, and corresponding 
numbers have been obtained for other elements by Gladstone 
and Haagen. The whole subject has been recently discussed 
and enriched with many new observations in an able memoir by 
Gladstone. As might be expected in so novel and recondite 
a subject, some anomalies occur which are difficult to explain. 
Thus hydrogen apyears in different classes of compounds with 
at least two refraction equivalents—one three times as great as 
the other, and the refra: tion equivalents of the aromatic com- 
pounds and their derivations as given by observation are, in 
general, higher than the calculated numbers. 
A happy modification of the ice calorimeter has been made by 
3unsen. ‘The principle of the method—to use as a measure of 
heat the change of volume which ice undergoes in melting—had 
already occurred to Herschel, and, as it now appears, still earlier 
to Hermann ; but their observations had been entirely overlooked 
by physicists, and had led fo no practical result. Bunsen has 
indeed clearly pointed out that the success of the method 
depends upon an important condition which is entirely his own, 
The ice to be melted must be prepared with water free from air, 
and must surround the source of heat in the form of a solid cylin- 
der frozen artificially zz szév. Those who have worked on the 
subject of heat know how difficult it is to measure absolute 
quantities with certainty, even where relative results of great 
accuracy may be attained. ‘The ice calorimeter of Bunsen will 
therefore be welcomed as an important addition to our means of 
research. Bunsen has applied his method to determine the 
specific heats of ruthenium, calcium, and indium ; and finds that 



the atomic weight of indium must be increased by one-half in 
order to bring it into conformity with the law of Dulong and 
Petit. He has also made a new determination of the density of 
ice, which he finds to be 0°9167. 5 , 
In a Report on the Heat of Combination which was made to 
this Association in 1849, the existence of a group of isothermal 
bases was pointed out. ‘* As some of the bases—potash, soda, 
baryta, strontia—” it was remarked, ‘‘ form what we may per- 
haps designate an isothermal group, such bases will develop the 
same, or nearly the same heat in combining with an acid, and no 
heat will be disengaged during their mutual displacements.” 
The latest experiments of Thomsen have given a remarkable 
extension to this group of isothermal bases. He finds that the 
hydrates of lithium, thallium, calcium and magnesium produce, 
when ail corrections are made, the same amount of heat on being 
neutralised by sulphuric acid, as the four bases before mentioned. 
The hydrate of tetramethylammonium belongs to the same class 
of bases. Ethylamin, on the other hand, agrees with ammonia, 
which, as has long been known, gives out less heat in combining 
with the acids than potash or soda. An elaborate investigation 
of the amount of heat evolved in the combustion of coal of diffe- 
rent kinds has been made by Scheurer-Kestner and Meusnier, 
accompanied by analyses of the coal. Coal rich in carbon and 
hydrogen disengages more heat in burning than coal in which 
those elements are partially replaced by oxygen. After deducting 
the cinders, the heat produced by the combustion of 1 gramme 
of coal varied from 8215 to 9622 units. 
Tyndall has given an extended account of his experimeuts on 
the action of a beam of strong light on certain vapours He 
finds that there is a marked difference in the absorbing power of 
different vapour for the actinic rays. Thus the nitrate of amyl 
in the state of vapour absorbs rapidly the rays of light competent 
to decompose it, while iodide of ally’ in the same state allows 
them freely to pass. Morren has continued these experiments in 
the south of France, and among other results he finds that sul- 
phurous acid is decomposed by the solar beam. 
Roscoe has prosecuted the photo-chemical investigations which 
Bunsen and he began some years ago. For altitudes above 10 
degrees the relation between the sun’s altitude and the chemical 
intensity of light is represented by a straight line. ‘Till the sun 
has reached an altitude of about 20 degrees, the chemical action 
produced by diffused daylight exceeds that of the direct sunlight. 
The two actions are then balanced ; and at higher elevations the 
direct sunlight is superior to the diffused light. The supposed 
inferiority of the chemical action of light under a tropical sun to 
its action in higher latitudes proves to be a mistake. According 
to Roscoe and Thorpe, the chemical intensity of light at Para 
under the equator in the month of April is more than three times 
greater than at Kew in the month of August. 
Hunter has given a great extension to the earlier experiments 
of Saussure on the absorptive power of charcoal fur gases. 
Cocoa-nut charcoal, according to Hunter’s experiments, exceeds 
all other varieties of wood charcoal in absorptive power, taking 
up at ordinary pressures 179 volumes of ammonia and 69 of car- 
bonic acid. Methylic alcohol is more largely absorbed than any 
other vapour at temperatures from 90° to 127°; but at 159°, the 
absorption of ordinary alcohol exceeds it. Cocoa-nut charcoal 
absorbs 44 times its volumes of the vapour of water at 127°. 
The absorptive power is increased by pressure. 
Last year two new processes for improving the manufacture of 
chlorine attracted the attention of the section; one of these has 
already proved to be a success, and I am glad to be able to state 
that Mr. Deacon has recently overcome certain difficulties in his 
method, and has obtained a complete absorption of the chlorine. 
May we hope to see oxygen prepared by a cheap and continuous 
process from atmospheric air? With baryta the problem can be 
solved very perfectly, if not economically. Another process is 
that of Tessier de Mothay, in which the manganate of potassium 
is decomposed by a current of superheated steam, and afterwards 
revived by being heated in a current of air. A company has 
lately been formed in New York to apply this process to the pro- 
duction of a brilliant house-light. A compound argand burner 
is used, having a double row of apertures, —the inner row is sup- 
plied with oxygen, the outer with coal gas or other combustible. 
The applications of pure oxygen, if it could be produced cheaply, 
would be very numerous, and few discoveries would more amply 
reward the inventor. Among other uses, it might be applied to 
the production of ozone free from nitric acid by the action of the 
electrical discharge, and to the introduction of that singular body 
in an efficient form into the arts as a bleaching and oxidising 
