12. In 1780 Scheele published his experiments on milk, and showed that sour milk contains a peculiar acid, to which the name oflacticacid has been given.He found that when sugar of milk is dissolved in nitric acid, and the solution allowed to cool, small crystalline grains were deposited. These grains have an acid taste, and combine with bases: they have peculiar properties, and therefore constitute a particular acid, to which the name ofsaclacticwas given. It is formed, also, when gum is dissolved in nitric acid; on this account it has been called,mucicacid.13. In 1781 his experiments on a heavy mineral called by the Swedestungsten, were published. This substance had been much noticed on account of its great weight; but nothing was known respecting its nature. Scheele, with his usual skill and perseverance, succeeded in proving that it was a compound of lime and a peculiar acid, to which the name oftungstic acidwas given. Tungsten was, therefore, a tungstate of lime. Bergman, from its great weight, suspected that tungstic acid was in reality the oxide of a metal, and this conjecture wasafterwards confirmed by the Elhuyarts, who extracted the same acid from wolfram, and succeeded in reducing it to the metallic state.14. In 1782 and 1783 appeared his experiments onPrussian blue, in order to discover the nature of the colouring matter. These experiments were exceedingly numerous, and display uncommon ingenuity and sagacity. He succeeded in demonstrating thatprussic acid, the name at that time given to the colouring principle, was a compound ofcarbonandazote. He pointed out a process for obtaining prussic acid in a separate state, and determined its properties. This paper threw at once a ray of light on one of the obscurest parts of chemistry. If he did not succeed in elucidating this difficult department completely, the fault must not be ascribed to him, but to the state of chemistry when his experiments were made; in fact, it would have been impossible to have gone further, till the nature of the different elastic fluids at that time under investigation had been thoroughly established. Perhaps in 1783 there was scarcely any other individual who could have carried this very difficult investigation so far as it was carried by Scheele.15. In 1783 appeared his observations on thesweet principle of oils. He observed, that when olive oil and litharge are combined together, a sweet substance separates from the oil and floats on the surface. This substance, when treated with nitric acid, yieldsoxalic acid. It was therefore closely connected with sugar in its nature. He obtained the same sweet matter from linseed oil, oil of almonds, of rape-seed, from hogs' lard, and from butter. He therefore concluded that it was a principle contained in all the expressed or fixed oils.16. In 1784 he pointed out a method by whichcitric acidmay be obtained in a state of purity fromlemon-juice. He likewise determined its characters, and showed that it was entitled to rank as a peculiar acid.It was during the same year that he observed a white earthy matter, which may be obtained by washing rhubarb, in fine powder, with a sufficient quantity of water. This earthy matter he decomposed, and ascertained that it was a neutral salt, composed of oxalic acid, combined with lime. In a subsequent paper he showed, that the same oxalate of lime exists in a great number of roots of various plants.17. In 1786 he showed that apples contain a peculiar acid, the properties of which he determined, and to which the name ofmalic acidhas been given. In the same paper he examined all the common acid fruits of this country—gooseberries, currants, cherries, bilberries, &c., and determined the peculiar acids which they contain. Some owe their acidity to malic acid, some to citric acid, and some to tartaric acid; and not a few hold two, or even three, of these acids at the same time.The same year he showed that the syderum of Bergman was phosphuret of iron, and theacidum perlatumof Proustbiphosphate of soda.The only other publication of Scheele, during 1785, was a short notice respecting a new mode of preparingmagnesia alba. If sulphate of magnesia and common salt, both in solution, be mixed in the requisite proportions, a double decomposition takes place, and there will be formed sulphate of soda and muriate of magnesia. The greatest part of the former salt may be obtained out of the mixed ley by crystallization, and then the magnesia alba may be thrown down, from the muriate of magnesia, by means of an alkaline carbonate. The advantage of this new process is, the procuring of a considerablequantity of sulphate of soda in exchange for common salt, which is a much cheaper substance.18. The last paper which Scheele published appeared in the Memoirs of the Stockholm Academy, for 1786: in it he gave an account of the characters of gallic acid, and the method of obtaining that acid from nutgalls.Such is an imperfect sketch of the principal discoveries of Scheele. I have left out of view his controversial papers, which have now lost their interest; and a few others of minor importance, that this notice might not be extended beyond its due length. It will be seen that Scheele extended greatly the number of acids; indeed, he more than doubled the number of these bodies known when he began his chemical labours. The following acids were discovered by him; or, at least, it was he that first accurately pointed out their characters:Fluoric acidTartaric acidMolybdic acidOxalic acidTungstic acidCitric acidArsenic acidMalic acidLactic acidSaclacticGallic acidChlorine.To him, also, we owe the first knowledge of barytes, and of the characters of manganese. He determined the nature of the constituents of ammonia and prussic acid: he first determined the compound nature of common air, and the properties of the two elastic fluids of which it is composed. What other chemist, either a contemporary or predecessor of Scheele, can be brought in competition with him as a discoverer? And all was performed under the most unpropitious circumstances, and during the continuance of a very short life, for he died in the 44th year of his age.
12. In 1780 Scheele published his experiments on milk, and showed that sour milk contains a peculiar acid, to which the name oflacticacid has been given.
He found that when sugar of milk is dissolved in nitric acid, and the solution allowed to cool, small crystalline grains were deposited. These grains have an acid taste, and combine with bases: they have peculiar properties, and therefore constitute a particular acid, to which the name ofsaclacticwas given. It is formed, also, when gum is dissolved in nitric acid; on this account it has been called,mucicacid.
13. In 1781 his experiments on a heavy mineral called by the Swedestungsten, were published. This substance had been much noticed on account of its great weight; but nothing was known respecting its nature. Scheele, with his usual skill and perseverance, succeeded in proving that it was a compound of lime and a peculiar acid, to which the name oftungstic acidwas given. Tungsten was, therefore, a tungstate of lime. Bergman, from its great weight, suspected that tungstic acid was in reality the oxide of a metal, and this conjecture wasafterwards confirmed by the Elhuyarts, who extracted the same acid from wolfram, and succeeded in reducing it to the metallic state.
14. In 1782 and 1783 appeared his experiments onPrussian blue, in order to discover the nature of the colouring matter. These experiments were exceedingly numerous, and display uncommon ingenuity and sagacity. He succeeded in demonstrating thatprussic acid, the name at that time given to the colouring principle, was a compound ofcarbonandazote. He pointed out a process for obtaining prussic acid in a separate state, and determined its properties. This paper threw at once a ray of light on one of the obscurest parts of chemistry. If he did not succeed in elucidating this difficult department completely, the fault must not be ascribed to him, but to the state of chemistry when his experiments were made; in fact, it would have been impossible to have gone further, till the nature of the different elastic fluids at that time under investigation had been thoroughly established. Perhaps in 1783 there was scarcely any other individual who could have carried this very difficult investigation so far as it was carried by Scheele.
15. In 1783 appeared his observations on thesweet principle of oils. He observed, that when olive oil and litharge are combined together, a sweet substance separates from the oil and floats on the surface. This substance, when treated with nitric acid, yieldsoxalic acid. It was therefore closely connected with sugar in its nature. He obtained the same sweet matter from linseed oil, oil of almonds, of rape-seed, from hogs' lard, and from butter. He therefore concluded that it was a principle contained in all the expressed or fixed oils.
16. In 1784 he pointed out a method by whichcitric acidmay be obtained in a state of purity fromlemon-juice. He likewise determined its characters, and showed that it was entitled to rank as a peculiar acid.
It was during the same year that he observed a white earthy matter, which may be obtained by washing rhubarb, in fine powder, with a sufficient quantity of water. This earthy matter he decomposed, and ascertained that it was a neutral salt, composed of oxalic acid, combined with lime. In a subsequent paper he showed, that the same oxalate of lime exists in a great number of roots of various plants.
17. In 1786 he showed that apples contain a peculiar acid, the properties of which he determined, and to which the name ofmalic acidhas been given. In the same paper he examined all the common acid fruits of this country—gooseberries, currants, cherries, bilberries, &c., and determined the peculiar acids which they contain. Some owe their acidity to malic acid, some to citric acid, and some to tartaric acid; and not a few hold two, or even three, of these acids at the same time.
The same year he showed that the syderum of Bergman was phosphuret of iron, and theacidum perlatumof Proustbiphosphate of soda.
The only other publication of Scheele, during 1785, was a short notice respecting a new mode of preparingmagnesia alba. If sulphate of magnesia and common salt, both in solution, be mixed in the requisite proportions, a double decomposition takes place, and there will be formed sulphate of soda and muriate of magnesia. The greatest part of the former salt may be obtained out of the mixed ley by crystallization, and then the magnesia alba may be thrown down, from the muriate of magnesia, by means of an alkaline carbonate. The advantage of this new process is, the procuring of a considerablequantity of sulphate of soda in exchange for common salt, which is a much cheaper substance.
18. The last paper which Scheele published appeared in the Memoirs of the Stockholm Academy, for 1786: in it he gave an account of the characters of gallic acid, and the method of obtaining that acid from nutgalls.
Such is an imperfect sketch of the principal discoveries of Scheele. I have left out of view his controversial papers, which have now lost their interest; and a few others of minor importance, that this notice might not be extended beyond its due length. It will be seen that Scheele extended greatly the number of acids; indeed, he more than doubled the number of these bodies known when he began his chemical labours. The following acids were discovered by him; or, at least, it was he that first accurately pointed out their characters:
Fluoric acidTartaric acidMolybdic acidOxalic acidTungstic acidCitric acidArsenic acidMalic acidLactic acidSaclacticGallic acidChlorine.
To him, also, we owe the first knowledge of barytes, and of the characters of manganese. He determined the nature of the constituents of ammonia and prussic acid: he first determined the compound nature of common air, and the properties of the two elastic fluids of which it is composed. What other chemist, either a contemporary or predecessor of Scheele, can be brought in competition with him as a discoverer? And all was performed under the most unpropitious circumstances, and during the continuance of a very short life, for he died in the 44th year of his age.