Potassium nitrate

"As a result of the whole tendency of this period pharmaceutical chemistry developed in the course of it to a marked extent. By reason of the eager search for new chemical preparations capable of employment as medicines, the apothecaries busied themselves more and more with chemical reactions, so that in their shops were reared the most important chemists of the following period. We shall find this... in the case of Kunkel, Marggraf, Geoffroy, and especially Scheele. Of inorganic compounds the salts in particular found general employment in medicine; potassium nitrate, , and were used under various names; , which was obtained by Glauber from the residue in the preparation of , and was called sal mirabile Glavberi, enjoyed great repute among the physicians of the time. Among ammonium salts, sal ammoniac and were employed, as well as and , discovered by Libavius and Glauber."

"If a vessel so prepared be filled with a solution of sugar and be then placed in water the water is found to pass through the membrane but the membrane is impermeable to the sugar. In consequence pressure termed osmotic pressure is found to occur within the pot and may be measured by suitable means. These osmotic pressures may at times be very large thus a 1 per cent. solution of sugar may exert a pressure of half an atmosphere and in the case of a solution of potassium nitrate of the same concentration it may amount to a couple of atmospheres."

"He Raymond Lully] was acquainted with nitric acid which he obtained by distilling a mixture of saltpetre and green vitriol. He mentions its power of dissolving, not merely mercury, but likewise other metals. He could form aqua regia by adding sal ammoniac or common salt to nitric acid, and he was aware of the property which it had of dissolving gold."

"The word nitre had been applied by the ancients to carbonate of soda, a production of Egypt, where it is still formed from sea-water by some unknown process of nature in the marshes near Alexandria. This is evident not merely from the account given of it by Dioscorides and Pliny; for the following passage from the Old Testament, shows that it had the same meaning among the Jews: "As he that taketh away a garment in cold weather, is as vinegar upon nitre: so is he that singeth songs to a heavy heart." Vinegar poured upon saltpetre produces no sensible effect whatever, but when poured upon carbonate of soda, it occasions an effervescence. When saltpetre came to be imported to Europe, it was natural to give it the same name as that applied to carbonate of soda, to which both in taste and appearance it bore some faint resemblance. Saltpetre possessing much more striking properties than carbonate of soda much more attention was drawn to it, and it gradually fixed upon itself the term nitre, at first applied to a different salt. When this change of nomenclature took place does not appear; but it was completed before the time of Roger Bacon, who always applies the term nitrum to our nitrate of potash and never to carbonate of soda."

"If a quantity of saltpetre be put into a crucible and raised to such a temperature as shall not merely melt it, but occasion an agitation in it like boiling, and if, after a certain time, the crucible be taken out of the fire and allowed to cool, the saltpetre still continues neutral; but its properties are altered: for, if distilled vinegar be poured upon it, red fumes are given out, while vinegar produces no effect upon the saltpetre before it has been thus heated. ...This young man was Scheele, who had informed Mr. Loock that there were two species of acids confounded under the name of spirit of nitre; what we at present call nitric and hyponitrous acids. Nitric acid has a stronger affinity for potash than vinegar has; but hyponitrous acid has a weaker. The heat of the fire changes the nitric acid of the saltpetre to hyponitrous: hence the phenomenon."

"The theory of combustion advanced by Dr. Hook, in 1665, in his Micrographia, approaches still nearer to that of Lavoisier than the theory of Rey, and indeed, so far as he has explained it, the coincidence is exact. According to Hook there exists in common air a certain substance which is like, if not the very same with that which is fixed in saltpetre. This substance has the property of dissolving all combustibles; but only when their temperature is sufficiently raised. The solution takes place with such rapidity that it occasions fire, which in his opinion is mere motion. The dissolved substance may be in the state of air, or coagulated in a liquid or solid form. The quantity of this solvent in a given bulk of air is incomparably less than in the same bulk of saltpetre. Hence the reason why a combustible continues burning but a short time in a given bulk of air: the solvent is soon saturated, and then of course the combustion is at an end. This explains why combustion requires a constant supply of fresh air, and why it is promoted by forcing in air with bellows. Hook promised to develop this theory at greater length in a subsequent work; but he never fulfilled his promise; though in his Lampas, published about twelve years afterwards, he gives a beautiful chemical explanation of flame founded on the very same theory. From the very general terms in which Hook expresses himself, we cannot judge correctly of the extent of his knowledge. This theory, so far as it goes, coincides exactly with our present notions on the subject. His solvent is oxygen gas, which constitutes one-fifth part of the volume of the air, but exists in much greater quantity in saltpetre. It combines with the burning body, and the compound formed may either be a gas, a liquid, or a solid, according to the nature of the body subjected to combustion."

"France... had been in the habit of importing her saltpetre, and her iron, and many other necessary implements of war: these supplies were suddenly withdrawn; and it was expected that France, thus deprived of all her resources, would be obliged to submit to any terms imposed upon her by her adversaries. At this time she summoned her men of science to her assistance, and the call was speedily answered. Berthollet and Monge were particularly active, and saved the French nation from destruction by their activity, intelligence, and zeal. Berthollet traversed France from one extremity to the other; pointed out the mode of extracting saltpetre from the soil, and of purifying it. Saltpetre-works were instantly established in every part of France, and gunpowder made of it in prodigious quantity, and with incredible activity. Berthollet even attempted to manufacture a new species of gunpowder still more powerful than the old, by substituting chlorate of potash for saltpetre; but it was found too formidable a substance to be made with safety."

"During the year 1796 he Smithson Tennant] made his experiments to prove that the diamond is pure carbon. His method was to heat it in a gold tube with saltpetre. The diamond was converted into carbonic acid gas, which combined with the potash from the saltpetre, and by the evolution of which the quantity of carbon, in a given weight of diamond, might be estimated."

"The Arabians possessed a very considerable knowledge of the acids, in comparison with that of the Ancients, who were totally unacquainted with the mineral acids. We already find Geber teaching in his treatise De Inventione Veritatis [On the Discovery of Truth] the method of obtaining nitric acid by distilling a mixture of saltpetre, copper vitriol, and alum in certain proportions; it was designated aqua dissolutiva or aqua fortis. Its preparation from saltpetre and sulphuric acid first became known to alchemists of a later date, but we find Basil Valentine speaking of it as a process which had been in operation for a long time."

"The important salts saltpetre, salmiac, and carbonate of ammonia, first became known and used for chemical purposes in the alchemistic period. Geber was well acquainted with potash saltpetre, as it served him for the preparation of nitric acid; and there is every reason to suppose that it was used in even earlier times for the production of fireworks and such like things, after its property of deflagrating with red-hot carbon had been recognised. The oldest designations for it were sal pctræ and sal petrosum. Raymund Lully also termed it sal nitri, but distinguished between it and nitrum, the fixed alkali of the older writers; in the sixteenth century this latter word was converted into natron, while nitrum was applied to potash saltpetre. Although Geber had already observed the formation of saltpetre from nitric acid and potash, the composition of this salt was only explained correctly at a much later date."

"Nitric acid also plays an important part in chemical industries, especially since the development of the manufacture of explosives on a large scale. Potassium nitrate, which has been known and valued for so long, is still an indispensable ingredient of gunpowder. Since the introduction of the nitrate of soda from the Chili deposits, nitric acid has been prepared from it (instead of from the more expensive nitrate of potash) by the old process of distillation with sulphuric acid. At the same time nitrate of soda is now largely converted into the potash salt by double decomposition with chloride of potassium. This process, so simple from a chemical point of view, could however only be carried out on an extensive scale after the rich deposits of potash salts at Stassfurt had been discovered; and it required careful chemical investigation to make those salts available, for their composition had to be worked out, and proper methods for separating them from one another had to be devised."

"The eighth century saw the planting of scientific culture in Spain, brought about through the founding of an Arab Caliphate at Cordova; whence sprung those famous universities of Cordova, Seville, and Toledo. It was at Seville, and in all probability during the second half of the eighth century, that the physician Geber carried on his great work. In his writings... are described for the first time the preparation of sulphuric acid by the distillation of alum, and of nitric acid by the action of this sulphuric acid on saltpetre. By the addition of nitric acid to salmiac he obtained the so called aqua regia. Geber, moreover, prepared potash and soda by the incineration of tartar and sea plants respectively, and by their action on his acids was led to the discovery of many new salts."

"While Paracelsus was pressing his doctrines on all sides, and endeavouring to lead chemistry into a new channel, another, Agricola, was quietly at work among the mines of Saxony, utterly indifferent to all but the advance of his science. It is to Agricola's systematic observations that we trace the beginnings of the science of mineralogy. In metallurgy, also, he was a pioneer, the first to give a clear and succinct account of the preparation of many metals. He taught the condensation and purification of sulphur given off during the roasting of many ores, the separation of silver from gold by means of nitric and sulphuric acid, the preparation of such bodies as salt, alum, and saltpetre on a large scale. The apparatus described by Agricola and employed by him for the smelting and testing of ores were still in use at the end of the eighteenth century. Agricola stands out solitary among the men of his time as one pursuing chemistry from pure love of the science; his work had no other aim than the increase of knowledge."

"Now Mayow, like Boyle, conceived the air as made up of minute particles, while he restricted himself to two varieties, those, namely, which are necessary to life, called by him "spiritus igno-aereus," and those incapable of supporting respiration or combustion, which are left after the removal of this "spiritus." Since a mixture of saltpetre and sulphur continued burning even under water, he assumed that his igno-aereal particles must also be contained in the salt. Acids too contained the new principle. ...Mayow died in 1679 at the age of thirty-four years; had he lived but a little longer, it can scarcely be doubted that he would have forestalled the revolutionary work of Lavoisier, and stifled the theory of phlogiston at its birth. As it was, his work, though rendered in one of the most luminous and convincing scientific publications of the period, was immediately forgotten, and so proved of little effect on the evolution of our modern chemical system."

"The famous 'Greek fire', which played so important a part in the defense of the Byzantine empire from the seventh century, had no precise formula, but its essential ingredient seems to have been naphtha... It appears that by the eleventh century the Chinese were aware that the incendiary properties of such mixtures could be much increased by the addition of nitre, the reason being that when it is heated this substance yields oxygen."

"By about 1300 mixtures of nitre, sulphur, and charcoal were being prepared for use in artillary and, later, in small arms. Of these three ingredients the preparation of the last two presented little difficulty. ...Nitre, however, presented much greater difficulties, for no pure material was readily available. The common source was earth from stables, pig-sties, and so-on, in which it resulted from bacterial action on manure. Generally, all the stable salts were extracted from the earth with boiling water, sometimes with the addition of potash or lime, and the resulting solution was boiled to concentrate it to the point at which ordinary salt, the most harmful impurity, separated out. The salt was removed and the solution allowed to cool, when crystals of pure nitre separated. The mixing of the three ingredients were both difficult and hazardous. It was difficult because a uniform and correctly balanced mixture was necessary for the best results, and hazardous because heat generated in the mixing process might cause explosion."

"Sulphuric acid was... necessary for the first stage of the Leblanc process... From the seventeenth century, Nordhausen in Saxony had been a centre for the manufacture of strong sulphuric acid by the distillation of green vitriol (ferrous sulphate), but the production there was limited and very expensive. Joshua Ward... had begun to manufacture it at Richmond in 1737 by burning a mixture of sulphur and nitre (saltpetre) in the necks of large vessels containing a little water: after several combustions, the water became converted into dilute sulphuric acid, which was then concentrated by distillation. Ward was granted a patent in 1749, even though his process was basically the same as one used experimentally by the German chemist John Glauber in the seventeenth century and his method was already being used in both France and Germany."