The three latter are elastic fluids, equal to 66.7 out of 126.7, or 1 f of the whole nearly. Mr Robins made the gaseous product of the whole. This last number, when the specific gravity of the gas is taken right, will differ very little from our calculation.
Now Mr Robins found that 27 grains of powder gene rated as much air as made of an atmosphere in a space equal to 520 cubic inches. This, at the pressure of the atmosphere, which was at the time equal to 30 inches, would make 34.6 cubic inches. The increased tempera ture which the receiver got by the explosion might re duce this to 30 or 31. We find from our calculation that 126.7 of gunpowder generates 169.6 cubic inches of gas. Then as 126.7: 27 : : 169.6: 35.7 cubic inches, which is only three cubic inches different from Mr Robins' experi ment. This might arise from his powder not consisting of proper proportions.
In the present improved state of chemical science, when the nature of the bodies constituting gunpowder are so well understood, as well as the compounds resulting from their action on each other, the proportions above given may be taken as the best for practice. The charcoal should, in particular, not be less in proportion to the nitre, as the smallest portion less than a whole atom would be the same as to leave out the whole atom, in which case there would be no carbonic oxide formed. If, for instance, instead of the, proportions 95.5 nitre, 16.2 charcoal, and 1"5 suipnur, the carbrIn was 16, then there would be 4.2 of carbon left in the resi,:, no carbonic oxide would be formed; since bodies cannot unite but in defi nite proportions.
The reason why carbonic oxide is formed during the decomposition of nitre by charcoal will be obvious from nitric acid having five atoms of oxygen. Four of these unite with two of carbon to form two atoms of carbonic acid, while the odd atom of oxygen is compelled to take another atom of carbon to form carbonic oxide. The writer of this article found the presence of the latter sub stance a fatal objection to getting pure carbonic acid by deflagrating nitre with charcoal.
The goodness of gunpowder is known to those expe rienced in it by its appearance. It should not be strictly black, but of azure grey inclining to red. The grains should appear uniform, both to the eye and to the touch. If some rub to powder sooner than others, it shows that the mass is not well mixed.
When it is fired on clean paper, or on a clean board, it should not soil it, or leave black spots. The smoke arising from it will form a circle or ring, more or less perfect as the explosion is more or less rapid, and is a good test of its strength.
The best and most certain test of the strength of gun powder is the elzrouvette. This is a machine in which the powder acts against a weight, in order to raise it to a given height. The powder in these machines, however, acts by a sudden impulse, and not as it acts in a gun, which is by gradual pressure during the whole time the charge is passing through the barrel. Hence the common powder powers are very imperfect, and have been lung deemed insufficient. The French method of trying powder is more to be depended upon, but it is more tedious, and takes up too much time for practice.
Each of the magazines for powder have a small mor tar, exactly of the same size, and capable of containing a ball of 71 inches in diameter. The mortar is elevated to an angle of 45° ; and when the powder is of the re quired strength, 3 ounces of it is capable of projecting the ball of the above size 55 French fathoms.
Mr Robins proposed a much more certain apparatus for trying the strength of powder, which has since been executed and reduced to practice by Dr Hutton. it is founded on the principle, that the momentum of the gun and the charge must be equal, or that the force of the powder, which is equally exerted upon both, will gene rate velocities in each, which will be inversely as their quantities of matter. Thus, if the weight of the charge were 1, that of the gun being 100, then their velocities will be reciprocally as these nu mkrs. For this purpose, Dr Hut ton's machi:ie consists of a brass cannon of about one inch bore.* Plate CCLXN XI V. Fig. 10, 11. It is suspended in such a way, that the arch of its recoil can be easily ascertained. The gun is generally charged with two ounces of powder. The arch of recoil gives the velocity with which it is propell ed, and hence the force or a given quantity of powder. No wadding is used in this method, the powder being merely collected into as compact a mass as possible. in these experiments, it should always be ascertained whether the whole of the powder be fired.