1ini\ unt oon iroM-iii gig •_' l Dii 'Itorteranftdjt bed >uv 



ncuii U,34o iWetei breilf. U l ♦ "■ > » iKctct t'du ,uu'oli>tc Dej 



Figure 2. — Galley-oven, 1869. The picture is a cross 

 section through the front of the oven showing one of the 

 36 retorts, the receivers for the distillate, and the space 

 in the upper story used for evaporating the mixture of 

 acid solution of calcium phosphate and coal. (According 

 to Anselme Payen, Precis de Chimie industrielle, Paris, 

 1849; reproduced from Hugo Fleck, Die Fabrikation 

 chemischer Produkte aus thierischen Abfdllen, Viewig, Brauns- 

 chweig, 1862, page 80 of volume 2, 2nd group, of P. 

 Bolley's Handbuch der chemischen Technologic.) 



Gottfried Hankwitz in the technique. Later on, 

 Jean Hellot (1685-1765) gave a meticulous descrip- 

 tion of the details and a long survey of the literature. 6 

 To obtain phosphorus, a good proportion of coal 

 (regarded as a type of phlogiston) was added to urine, 

 previously thickened by evaporation and preferably 

 after putrefaction, and the mixture was heated to the 

 highest attainable temperature. It was obvious that 

 phlogiston entered into the composition of the distil- 

 lation product. The question remained whether this 

 product was generated de novo. In his research of 

 1743 to 1746, Andreas Sigismund Marggraf (1709- 

 1 782) provided the answer. He found the new sub- 

 stance in edible plant seeds, and he concluded that it 

 enters the human system through the plant food, to be 

 excreted later in the urine. He did not convince all 

 the chemists with his reasoning. In 1789, Macquer 

 wrote: "There are some who, even at this time, hold 

 that the phosphorical ('phosphorische') acid generates 



itself in the animals and who consider this to be the 

 'animalistic acid.' " ' 



Although Marggraf was more advanced in his argu- 

 ments than these chemists, yet he was a child of his 

 time. The luminescent and combustible, almost wax- 

 like substance impressed him greatly. "My thoughts 

 about the unexpected generation of light and fire out 

 of water, fine earth, and phlogiston I reserve to de- 

 scribe at a later time." These thoughts went so far as 

 to connect the new marvel with alchemical wonder 

 tales. When Marggraf used the "essential salt of 

 urine," also called sal microcosmicum, and admixed 

 silver chloride ("horny silver") to it for the distillation 

 of phosphorus, he expected "a partial conversion of 

 silver by phlogiston and the added fine vitrifiable 

 earth, but no trace of a more noble metal appeared." 8 



Robert Boyle had already found that the burning 

 of phosphorus produced an acid. He identified it by 

 taste and by its influence on colored plant ex- 

 tracts serving as "indicators." Hankwitz 9 described 

 methods for obtaining this acid, and Marggraf showed 

 its chemical peculiarities. They did not necessarily 

 establish phosphorus as a new element. To do that 

 was not as important, at that time, as to conjecture 

 on analogies with known substances. Underlying 

 all its unique characteristics was the analogy of 

 phosphorus with sulfur. Like sulfur, phosphorus can 

 burn in two different ways, either slowly or more 

 violently, and form two different acids. The analogy 

 can, therefore, be extended to explain the results in 

 both groups in the same way. In the process of 

 burning, the combustible component is removed, and 

 the acid originally combined with the combustible 

 is set free. Whether the analogy should be pursued 

 even further remained doubtful, although some sus- 

 picion lingered on for a while that phosphoric acid 

 might actually be a modified sulfuric acid. Analogies 

 and suspicions like these were needed to formulate 

 new questions and stimulate new experiments. They 

 are cited here for their important positive value in 

 the historical development, and not for the purpose of 

 showing how wrong these chemists were from our 



6 Jean Hellot, Mlmoires Acadlmie 1737 (Paris, 176G), under 

 date of November 13, 1737. pp. 342-378. 



' Macquer, op. cit. (footnote 3), p. 551. 



" A. S. Marggraf, Akademie der li'issenschaften, Miscellanea 

 Berolinensia (Berlin, 1743), vol. 7, 342 fT. ; see also WlLHELM 

 OSTWALD hlassiker der Exaklen Natv.rwissenscha.jten (Leipzig: 

 Engelmann, 1913), no. 187. 



9 G. Hanckewitz, [Hankwitz], Philosophical Transactions of the 

 Rural Society of London, 1724-1734, abridged (London, 1809), 

 vol. 7, pp. 596-602. 



180 



BULLETIN 240: CONTRIBUTIONS FROM THE MUSEUM OF HISTORY AND TECHNOLOGY 



