Contributions of Charles Hatchett

Most of his scientific research was done during the decade 1796 to 1806. His first paper in the Philosophical Transactions described his analysis of the Carinthian lead molybdate (4). The celebrated Scheele, said he, in 1778 read before the Academy of Sciences at Stockholm an essay in which he proved. . . that the mineral called Molybdaena was composed of sulfur and a peculiar metallic substance, which, like arsenic and tungsten, was liable by super-oxygenation to be converted into a metallic acid which in its properties differed from any other that had been previously discovered. Hatchett mentioned the confirmatory researches of B. Pelletier, P. J. Hjelm, and Mr. Islmann [J. C. Ilsemann], and added But the existence of this substance was known to be only in that mineral which Scheele had examined. This lead mineral from Carinthia had been described by the Abbe F. X. Wulfen and by N. J. Jacquin. For several years it was believed to be lead tungstate, but Klaproth proved it to be lead molybdate. Since Klaproth had had an insufficient amount of the mineral, Hatchett made a complete analysis of it and investigated the properties of molybdic add. 

In the following year Hatchett was made a Fellow of the Royal Society. In 1798 he analyzed an earthy substance, sydneia, which Josiah Wedgwood had found in New South Wales and another specimen of it provided by Sir Joseph Banks (5). This, according to Wedgwood, was composed of a fine white sand, a soft white earth, some colourless micaceous particles, and some which were black. Hatchett found it to consist of siliceous earth, alumine, oxide of iron, and black lead or graphite and concluded that the Sydneian genus, in future, must be omitted in the mineral system.  

In the following year Sir Everard Home interested Mr. Hatchett in the chemical composition of dental enamel (7, 8). Since the tooth of the elephant is composed of three different structures, Sir Everard wished to know whether the materials themselves were different or only differently arranged. Hatchett showed that the enamel was composed of calcium phosphate. The enamel, said he, has been supposed not a phosphate but a carbonate of lime. This error may have arisen from its solubility in acetous acid or distilled vinegar but the effects of the acetous acid are in every respect the same on powdered bone as on the enamel (8). 

Hatchett then investigated the composition of shell and bone. When it is applied to the cuttle-bone of the shops. . . , said he, the term bone is here misapplied. .. for this substance in composition is exactly similar to shell, and consists of various membranes hardened by carbonate of lime, without the smallest mixture of phosphate (8). 

Hatchett observed that the external skeleton of crustaceans and the egg shells of birds contain more calcium carbonate than calcium phosphate but that in bones the phosphate predominates. It is possible, said he, .. . that some bones may be found composed only of phosphate of lime and that thus shells containing only carbonate of lime and bones containing only phosphate of lime will form the two extremities in the chain.. . .  

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Weeks, M. E., The chemical contributions of Charles Hatchett, J. Chem. 

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