ia : 
Oct. 2, 1873 | : 
of the molecules in the line of sight. If there is any 
truth at all in the kinetic theory of gases, the molecules of 
sodium, or whatever the substance may be, are moving in all 
directions indifferently, and with velocities whose magnitudes 
_ cluster about a certain mean. The law of distribution of velo- 
_ Cities is probably the same as that with which we are familiar in 
__ the theory of errors, according to which the number of molecules 
affected with a given velocity increases, the nearer that velocity 
is to the mean. 
___ By the principles of this theory of gases the mean square of the 
velocity of the molecules can be deduced from the known pres- 
sure and mass. If wv denote the velocity whose square is equal 
to the mean, it is found that for air at the freezing-point, v = 485 
metres per second. 
At the temperature of flame, the velocity may be about three 
times greater. For the purposes of a rough estimate it will be 
accurate enough to take the mean velocity of the molecules at 
1,500 metres per second, and that of light at 300,000,000 
metres per second. The wave-length of the light emitted by a 
molecule moving with the mean velocity from the eye will therefore 
be ter by about five millionths than if the molecule were 
atrest. The double of this will be a moderate estimate of the 
width.of the spectral line, as determined by the cause under con- 
sideration. We may conclude that however rare the gas, and 
however perfect our instrument may be, a fixed line cannot be 
reduced to within narrower limits than about a hundredth part of 
_ theinterval between the sodium lines. I must leave it to spectro- 
_ scopists more practised and skilful than myself to say whether 
this result is in agreement with the appearance of the spectrum, 
SECTION B.—CuHEMISTRY 
The report of the Committee appointed to examine the 
Methods of making Gold Assays and stating the Results thereof, 
was read by Mr. W. C. Roberts. 
The report stated that although the amount of alloy in gold 
could be ascertained to within a maximum error of o’o! per cent., 
or one ten-thousandth part, yet there was an amount of differ- 
ence between the results obtained by different assayers which 
required an explanation. The committee considered that the 
difference between different assayers was too great to be ac- 
counted for by the ordinary causes of error in analysis, and they 
had therefore come to the conclusion that the nominally assayed 
gold must have contained some impurity which had escaped the 
assaying process. The committee had precipitated eighty ounces 
of gold from no less than a hundred gallons of chloride of gold, 
and they suggested that the gold thus ohtained might be used 
as a standard with which the gold assayed by different assayers 
might be compared. 
Mr. A. Vernon Harcourt, F.R.S., and Mr. F. W. Fison, 
F.C.S., explained a Continuous Process sor Furifying Coal Gas 
and oblaining Sulphur and Ammonium Sulphate. 
Mr. Vernon Harcourt said that the usual method of freeing 
coal gas from sulphuretted hydrogen was by passing it through 
lime. But oxide of iron was also employed in place of the lime, 
the advantage possessed by the oxide being that whilst the lime, 
after it had served its purpose, was useless and difficult to get rid 
of, the oxide of iron could be used repeatedly for the same purpose. 
The chemical changes involved were, that when the gas had 
passed through the oxide the latter was changed into sulphide of 
iron ; when the sulphide was exposed to the air, the sulphur 
separated and the oxide was re-formed, thus enabling the oxide 
to be again used. This was called a continuous process, because 
the oxide could be continuously used. But the process was not 
quite continuous, for after the oxide had been used some thirty 
times, it became so clogged with sulphur as to be useless. The 
advantage of the process he was about to describe was that the 
oxide could be used over and over ad infinitum ; and, besides, 
the ammonia was secured in a marketable form. The present 
method of freeing gas from ammonia by “‘ scrubbing,” or passing 
it through a large receiver containing a small quantity of water 
spread over a large surface, had one or two defects. It did not 
secure the ammonia in a good form, and it probably diminished 
the illuminating power of the gas, for olefiant gas was soluble in 
water. The new process was applicable wherever oxide of iron 
could be used in the purifying process. The difference from 
the old process was that the oxide during revivification was 
moistened with a solution of ferric sulphate (per sulphate of iron), 
NATURE 
: I 
would still have a finite width, in consequence of the motion 
a Mee eee a 
< aSe 
475, 
and a portion of the oxide was removed from time to time, and 
treated as follows :—It was first extracted with water by the use 
of a well-known arrangement. The soluble salts were sulphate 
of ammonia—formed in the purification by the reaction of am- 
monia upon ferric sulphate—and, in smaller quantities, sulpho- 
cyanide, hypo-sulphite, and probably sulphate of ammonia. 
This extract was mixed with a small excess of sulphuric acid ; 
and yielded when concentrated by evaporation, crystals of am- 
monium sulphate. The remainder of the substance was then 
boiled with dilute sulphuric acid, which dissolved the oxide and 
left a residue of sulphur. The actual process of extraction by 
acid consisted in treating the substance successively with (1) a 
solution of ferric sulphate containing some free sulphuric acid ; 
(2) with a more dilute solution of ferric sulphate to which 
sulphuric acid had been added ; (3 and 4) with more dilute 
solutions of ferric sulphate—all these liquids being the product 
of a former extraction—and (5) with water. The liquid resulting 
from the first of the treatments enumerated above was a strong 
solution of ferric sulphate, which was used as already mentioned, 
by being mixed with the charge of oxide before it was replaced 
in the purifier. The residue of the final washing consisted 
almost entirely of sulphur, and required only to be dried. It 
would be evident that all the oxide which had been freed from 
sulphate of ammonia and sulphur by this treatment passed into 
the condition of ferric sulphate, and in this condition it was 
replaced in the purifier. There it again became oxide by the 
action upon it of the ammonia in the gas, which it completely 
removed, fixing it as sulphate. This system had been brought 
into use as a manufacturing process, and had been found to be, as 
far as could be judged, a complete success. 
Mr. Fison explained at length the apparatus by which the pro- 
cess was carried into effect. 
Mr. J. Spiller, F.C.S., gave a short communication on 4rfi= 
ficial Magnetite, the object of which was, first, to point out an 
error in the statement of a chemical reaction occurring in several 
standard works of reference ; and, in the second place, to indi- 
cate the formation of crystallised magnetic oxide of iron (mag- 
netite) in the ordinary process of manufacturing aniline from 
nitro-benzol by the reducing action of metallic iron. Reference 
was made to ‘‘ Reimann’s Aniline and its Derivatives,” and to 
Wagner’s ‘‘Chemical Technology,” where the action of iron upon 
nitrobenzol in the presence of acid (Béchamp’s process) is stated 
to give ferric oxide, or a ‘‘ hydrated oxide of iron.” The author 
pointed to the fact that the ordinary residual product in this 
operation was é/ack, and could be so far purified by washing and 
eJutriation from the excess of iron, usually remaining in ad- 
mixture, as to give a fine black pigment, which appeared under 
the microscope as minute octohedra, and was strongly magnetic. 
Chemical analysis showed this to consist almost entirely of mag- 
netic oxide of iron, with such impurities as were inherent to the 
process, or previously existed in the cast iron. The physical 
properties of this form of oxide were further described, and its 
analogy to the native varieties of magnetic ore (Commish and’ 
Dannemora) shown, 
Mr. W. C, Roberts exhibited some specimens of artificial 
horn silver which he had formed by mixing strong solutions of 
silver nitrate and common salt. 
Prof. Schafarick, of Prague, read a paper Ox the Constitution of 
Silicates, in which he developed his views as to the manner in 
which certain members of this class of bodies might be graphically 
represented.—Prof. Crum Brown, whilst complimenting the 
author on the importance of the step taken, pointed out that we 
should guard against confusing graphic formulz, as applied to 
minerals, with those applied to organic substances, because they 
do not represent the same kind of knowledge. Structural for- 
mulze in organic substances represented reactions, and not merely 
composition ; in the case of minerals we had as yet no method 
of following their reactions. 
Prof. Crum Brown then read a paper On the Action of Sul- 
phide of Methyl on Bromacetic Acid. We said bromacetic acid 
dissolved readily in sulphide of methyl. The solution soon be- 
came warm and separated into two layers, the lower of which 
solidified into a white crystalline mass. The crystals were easily 
purified by washing with absolute alcohol, in which they were 
very sparingly soluble. Analysis had given a result for this 
compound which showed it to be a compound of one molecule of 
bromacetic acid, and one ofsulphide of methyl. The compound 
was obviously analogous to hydrobromate of betain. 
Mr, Jesse Lovett described an improved gas-burner, 
