608 
NATURE. 
[JuLy 29, 1915 

replaced by the radical nitryl, NO,, and it forms with | L é : 
' really the best of the high explosives, and although it 
metals a class of salts called ‘‘ picrates.’’ The potass- 
ium salt was suggested as a bursting charge for shells 
nearly fifty years ago, whilst Sprengel showed that 
picric acid itself could be detonated, and later 
Turpin employed the acid as an explosive. It 
was found possible to get a great weight of explosive 
into a small space, as the acid could be melted and 
poured into the shell in a molten condition. Picric 
acid per se is a very safe explosive, but has the draw- 
back of acting on metals to form picrates, some of 
which are far more sensitive to disturbing influences 
than the acid itself. 
Experiences with lyddite shells in the South African 
war showed their behaviour to be very erratic, some 
exploding with great effect, whilst others gave dis- 
appointing results, this being due to the fact that picric 
acid requires a powerful detonator for obtaining the 
highest explosive effect, and the use of such a de- 
tonator was dangerous, and might cause a premature 
explosion of the shell within the gun. 
The disadvantages inherent in the use of picric acid 
led to attempts being made to replace it by some other 
material of the same character, which could be used 
as a high explosive in a bursting charge and yet be 
free from these drawbacks. Such a body was 
found in trinitrotoluol, and although its explosive force 
is slightly less than that of picric acid, the pressure 
of the latter being 135,820 Ib. on the square inch, as 
against 119,000 for trinitrotoluol, yet its advantages 
more than compensate for this difference. Not being 
of an acid nature, trinitrotoluol, or T.N.T., as it is 
termed, cannot accidentally form more sensitive salts; 
it is without action on metals, and is perfectly stable. 
The formation of volumes of black smoke on de- 
tonation of the T.N.T. has given rise to the names 
given to shells containing this explosive of ‘ Black 
Marias,"’ “‘coal-boxes,’”’ and ‘Jack Johnsons,’ and 
the fact that this cloud of carbonaceous matter is pro- 
duced shows conclusively that the oxygen contained 
in the nitryl radical present in the explosive is in- 
sufficient for its complete combustion. An excellent 
explosive used during the Balkan war, and now 
largely employed by the Austrians, is known as 
ammonal, in which 12 to.15 per cent. of T.N.T. is 
mixed with an oxidising compound, ammonium 
nitrate, a little aluminium powder, and a trace of char- 
coal. This mixture gives even better results than the 
T.N.T. alone, and its only drawback is the hygro- 
scopic character of the ammonium nitrate, which 
necessitates the material being made up in air-tight 
cartridges. It forms, however, a most effective burst- 
ing charge, and although the rate of detonation of 
the trinitrotoluol is reduced by the admixture of the 
oxidising compounds, the shattering effect is even 
more destructive than when the explosive is used 
alone, as the pieces of shell scattered are larger in 
size. An improved form of this explosive is being 
made 6n a large scale in England for use by the Allies, 
and renders the supply of high explosives for shells 
perfectly adequate. 
Toluene is obtained from the crude benzol in coal tar 
and by scrubbing coal gas, by fractional distillation, 
and is also being produced synthetically from other 
hydrocarbons by the action of heat and pressure, so 
it is safe to say that any requirements for toluene 
to nitrate can be amply met. 
Under the influence of nitration other constituents 
of tar are converted into effective explosives, dinitro- 
benzol being the basis of such mining explosives as 
‘“Roburite’’ and “ Bellite,’’ whilst trinitrocresol has 
been used largely in place of picric acid, under the 
name of ‘‘Ecrasite,” but it shares with picric acid the 
drawbacks of forming more sensitive compounds with 
bases and of having an acid reaction. 
nom, 1287, VOL. 95] 

Expert opinion has by no means settled which is 
was the Germans who were chiefly responsible for 
bringing T.N.T. into such prominence, there are not 
wanting signs that they are largely reverting to picric 
acid, 
Probably the most powerful explosive known _ is 
made from benzene by converting it into anilin, and 
by nitration making this into tetranitro-anilin, an 
explosive of which a great deal more will be heard, 
whilst another derivative tetranitromethylanilin, 
known as “‘tetryl,” is being used largely for primers 
and detonators. 
I1J.—Potson Gas anD INCENDIARY Bombs. 
There are many gases known which are irrespirable. 
Some, like carbon dioxide, nitrogen, and hydrogen, act 
merely in the same way as water would do by cutting 
off the oxygen supply, which is a necessity to life, 
from the lungs, but have no toxic action on the 
system. Other gases, like carbon monoxide and 
cyanogen, are powerful poisons, less than 1 per cent. 
of which in the air will cause death by purely toxic 
action. Others again, like sulphur dioxide, chlorine, 
and bromine, may act by producing spasms of the 
glottis, and subsequent asphyxiation. 
The use of asphyxiating gas is by no means the 
simple problem that one might imagine. In the first 
place, gases differ from other forms of matter in that 
the molecules of which they consist being free from 
cohesion, are able to intermingle, no matter how 
different may be their weights, a process which is 
known as “diffusion,” so that unless the gas is very 
considerably heavier than air it intermingles with the 
atmosphere so quickly as to prevent its spreading in 
a poisonous quantity over any considerable area. No 
gas which is not more than double the weight of air 
could be used effectively in sufficient quantity to be 
poisonous at the distances likely to exist between the 
trenches. It is this that accounts for the fact that 
although 1 per cent. of carbon monoxide is instantly 
fatal, no deaths can be traced to its effects during the 
war, although all our propellants and high explosives 
give on explosion large volumes. 
The weight of a gas is represented by its density, 
that is, how many times it is heavier than hydrogen, 
the lightest gas known, and in the following table 
are shown the densities of the various gases suspected 
of having been used or possible to use, and the relation 
of their weight to an equal volume of air :— 
Times 
Density heavier 
than air 
Sulphur dioxide ... meng 2°21 
Nitrogen tetroxide 46 3707, 
Chlorine Bs soo: SO 2°45 
Bromine vapour ... eco 553 
Phosgene 50°6 3°49 
By the laws of diffusion gases intermingle at a rate 
which is inversely proportional to the square roots of 
their densities, but air currents or wind enormously 
increase the rate of admixture, so that with anything 
like a breeze blowing it would be impossible to use — 
them successfully, whilst the opportunity for ‘ fright- 
fulness”’ is, of course, limited by the direction of the 
wind, so that in Flanders it is only with the wind 
in the north or a point or two on either side that 
effective use could be made of them. 
During the past few months the prevailing winds 
have been in the enemy’s favour for considerably more 
than the normal period, and it is to be hoped that 
during the next few months with the prevalent wind 
from the south or south-west the opportunity of using 
these gases will be reduced to a minimum. 

