Hutton shows that gunpowder is but so much condensed air; for he says “We may hence, also, deduce the amazing degree of condensation of the elastic air in the nitre and gunpowder, and the astonishing force experienced by its explosion. It has been found by Mr. Robins, and other philosophers, that 3-10ths of the mass of the powder consists of the pure condensed air, or that the weight of the condensed air is equal to 3-10ths of the whole composition. But the whole composition of the powder consists of eight parts by weight, of which six parts are nitre, one part sulphur, one charcoal; of which the nitre or 3-4ths of the composition furnishes the whole of the condensed air, while the sulphur and charcoal only give the fire that produces the explosion. But 3-10ths of the whole mass of eight parts is equal to 4-10ths of the six parts of nitre, that is 4-10ths or 2-5ths of the nitre consists of condensed air, or the weight of the gross matter in the nitre as four to six, or as two to three; and these two parts, it is probable, are of equal density or specific gravity. Yet the specific gravity of nitre is 1,900, that of water being 1,000, and of air 1·2, which is contained in 1,900, as much as 1,583 times; that is, the air in the nitre must be condensed the amazing quantity of 1,583 times, if its specific gravity be equal to the compound nitre itself.” Also, “The air is condensed in the nitre about 1,600 times, nearly double the density of water, which may well be considered as probably the greatest degree of compression that air is capable of. Hence it may be perceived that a prodigious force must be exerted by nature in generating nitre; and as this great force actually exists in nature, it is very probable that the air in the nitre is thus compressed into the most dense state possible, and in this consists the similitude among the different particles of nitre.” This extract from Hutton enables us to divest the question of any technicalities, and puts it in so plain a garb that the simplest mind may comprehend it. Now, the great improvement of chemistry has been to extract from the nitre the gross material which is contained in the proportions--2-5ths impurities, and 2-5ths condensed air; thus, half the quantity being useless, the extraction of these alloys gives a greater quantity of condensed gases in the same quantity of matter; for if we take away 2-5ths of the proportions of useless matter, and supply its place with 2-5ths more condensed air, we thus get 4-5th explosive matter in the same bulk of material, and thus simply obtain an immense increase of power without an increase in bulk. We have here evidence of the progress that has been made in the science of explosive force.