304 
NATURE 
be tolerably even. It is advisable to have the ground 
next the curb well trodden on and rammed _ before 
the pavement is laid, otherwise there will be an 
unseemly hollow next the curb. In laying, the rough 
stuff is put down first and rolled tolerably firm, then 
the second quality is put on, then the third, and when the 
whole has been raked level, a little of the finest material 
is sifted on through a sieve with $-in. meshes, and a litile 
fine white shingle or Derbyshire spar is sprinkled on the 
top. The whole must now be well rolled. The best roller 
is a water ballast roller, which at first is used without 
ballast, and well wetted to prevent adhesion of the material, 
and, when the pavement is slightly consolidated, the full 
weight should be applied. 
For heavy cart traffic the material should be made of 
shingle only, heated and mixed as above, and well rolled. 
Both descriptions of pavement are laid best and most 
easily in warm weather, and should be rolled when the 
sun has warmed it well. Those parts in angles should be 
well rammed and trimmed off with a light shovel. 
Though apparently a simple manufacture, there is a 
little difficulty in ascertaining the proportion of tar to 
gravel or cinder-dirt. A little experience will only be 
necessary in this, as well as in all other manufactures, to 
enable anyone to carry it out successfully. 
This pavement cannot be spoken of too highly, as it is 
cheap, wears well, and can be easily repaired. The colour, 
which never can be made to equal York flag, and the 
smell for some time after it is laid, are the only objections 
to its use; it can be laid witha good profit in any dis- 
trict at 1s. 4d. per square yard ; and besides being a boon 
to the public, who must otherwise walk on gravel, isa 
great advantage to gas companies. To them it provides 
a remunerative outlet for their tar, which often otherwise 
must be sold at a low price to distant distillers. 
A late paragraph, which appeared in the daily press, 
states that it is proposed to pave the streets of London 
with stone laid in asphalte instead of lime grout. This is 
just a more systematic application of the above-described 
plan ; for the tar, by being boiled and thrown on hot 
stones, becomes an elastic asphalte. 
INDIAN BARRACKS 
ECENT discussions regarding the new Indian 
Barracks have shown the necessity for an adequate 
knowledge of physical science on the part of all engineers 
who have to cope with great natural forces. 
These costly structures have been described as ‘sun 
traps,” meaning thereby that the materials and details have 
been so selected, that instead of the interior of the rooms 
being as cool as, if not cooler, than the outside, it is cooler 
for the men to be in the open air under thesun. It is true 
that this objection has been raised at very few stations, but 
with adequate knowledge on the part of the architects, 
it ought never to have been raised at all. The barracks 
complained of are stated to be brick structures of the 
usual dark colour, with verandahs supported not on light 
easily heated and easily cooled columns, but on massive 
piers and arches like a bridge. The roofs have been 
constructed almost as they would have been at home, and 
no adequate means have been adopted for protecting the 
walls from sun-radiation. Of course the great mass of 
brickwork becomes heated during the day, and heats the 
air outside and inside the rooms at night, while the struc- 
ture of the roof is such that the interior is heated both by 
direct conduction and radiation. Now surely such mistakes 
might have been avoided. There are such things as non- 
conducting materials to be had, and double walls with aven- 
tilating air space between are not an uncommon expedient 
in this country for keeping out both heat and cold. Again, 
there is such a thing as white plaster or whitewash for 
outside walls, which refiects a large portion of the solar 
heat. Double roofs are not unknown, we believe, in India, 
(73 
| Aug. 11, 1870 
and it is possible to construct such a roof as to interpose 
not only an air current between the outer and inner layer 
of the roof, but to prevent the radiation of the inner surface 
of the outer layer passing through the inner layer. These 
are very elementary applications of physical laws to Indian 
house construction, and how little they have been at- 
tended to may be inferred from a fact which has been 
stated—viz., that these barracks have been roofed with 
slate. The ordinary laws of conduction and radiation of 
heat appear to be ata discount in the Indian works de- 
partment. 
THE PROVINCE OF MINERAL CHEMISTRY 
(DEC eso KOLBE has recently succeeded to the 
directorship of the Fournal fiir Praktische Chemie, 
rendered vacant by the decease of Erdmann, its original 
founder ; and in his hands this periodical will doubtless 
become the recognised organ of the modern Leipsic 
School of Chemistry. Dr. Kolbe, in the first number o 
the new series of this work, has signalised his succession 
to the office of editor by an introductory essay, setting 
forth his opinions upon what he considers must be the 
future aim of the student of Inorganic Chemistry. Or- 
ganic Chemistry, once the neglected sister of Inorganic 
Chemistry (to use the Professor’s- phraseology), has be- 
come so courted and honoured since Liebig introduced 
her as a young science into the chemical world, that 
little by little her relative has sunk into comparative ob- 
scurity. But the time has now arrived when, in Kolbe’s 
opinion, it is evident that Inorganic Chemistry has not 
merited this neglect, but that she has it in her power to 
bestow rewards not less precious than those of Organic 
Chemistry, upon those who devote themselves to her 
service. 
Much of the attractiveness of Organic Chemistry must, 
according to Kolbe, be traced to the zeal with which the 
origin of the almost numberless cases of Isomerism in 
organic compounds is being searched out ; indeed, this 
zeal has nearly displaced the lively interest in Inorganic 
Chemistry created by the discovery of Isomorphism. 
This cause can never actuate the investigator in the 
domain of Inorganic Chemistry—at least not to the same 
extent—and for the reason adduced by Kolbe, that Iso- 
merism cannot possibly occur in inorganic compounds 
to anything like the same degree as among organic sub- 
stances, owing to the greater simplicity of constitution 
possessed by the former class. That so few cases of 
Isomerism have been discovered in Inorganic Chemistry 
is undoubtedly due to the fact that hitherto we have 
neglected to investigate mineral substances with special 
regard to their chemical constitution. 
In order to prove the truth of this latter assertion Kolbe 
asks how can we frame anything like a reply to any ques- 
tion respecting the chemical constitution of the naturally- 
occurring silicates—felspar, forexample? What are the 
proximate constituents of this compound, and what are 
their respective functions ? 
In half a dozen brief sentences Kolbe disposes of all 
our knowledge upon this subject, beginning with the views 
of Berzelius, by whom felspar—the typical silicate—was 
regarded as possessing a constitution analogous to that of 
dehydrated alum—that is, as a double salt of neutral 
silicate of alumina and silicate of potash ; and ending 
with Gerhardt, who thought to explain the constitution 
of this and all bodies by his theory of types, or, in the 
expressive language of Professor Kolbe—“mit der 
mechanischen Handhabung eines todten Schematismus.” 
The greater portion of the paper is devoted to Kolbe’s 
theoretical views upon the nature of felspar, and he sug- 
gests anumber of structural formule to explain its con- 
stitution according to our present opinions upon the 
quantivalence of the component elements. Whether, 
however, any of these formule represent the actual con- 
