436 SCIENCE PROGRESS 



analogy. Its literature was replete with wild allegories expressed 

 in an obscure jargon which served to conceal the meaning from 

 the uninitiated. The alchemists, nevertheless, gleaned many 

 facts which form the groundwork of chemistry, and we owe to 

 them many useful materials, chemical processes, and pieces 

 of apparatus. In mediaeval times many of them were able, 

 honest, and even religious men ; some may indeed be justly 

 regarded as the great men of their day ; but by the seventeenth 

 century the cult had degenerated into charlatanism, and the 

 adepts were fraudulent quacks who trafficked in the philosopher's 

 stone, which was supposed to have the power of turning base 

 metals into gold, and the elixir of life, which was said to cure 

 every ill and to prolong life indefinitely, preserving perpetual 

 youth. 



In Wright's time alchemy was to a great extent discredited, 

 but the birth of chemistry was retarded by the phlogiston 

 theory, a false theory of combustion which regarded flame as an 

 elementary substance. The composition of air and water, 

 hitherto considered as elements, and the chemistry of the gases 

 of which they consist, were being investigated by his contem- 

 poraries Black, Priestley, and Cavendish, who still expressed 

 their results in terms of the phlogiston theory. Towards the 

 close of the century the French chemist Lavoisier promulgated 

 the doctrine that the gases oxygen, nitrogen, and hydrogen 

 were elements, and that the process of combustion could be 

 perfectly explained without assuming the existence of phlogiston. 

 After considerable controversy his views were generally ac- 

 cepted ; henceforth chemistry was freed from the shackles 

 of the phlogiston theory, and the foundations of the modern 

 science were made secure. 



The subject of the picture is the discovery of phosphorus, 

 which was first obtained accidentally by a citizen of Hamburg 

 named Brandt, about a century previously in the course of his 

 search for the philosopher's stone. The details of the process 

 were kept secret for many years, but an adequate account was 

 published earlier in the eighteenth century. With this descrip- 

 tion Wright was obviously familiar. The materials from which 

 the phosphorus was prepared were strongly heated in a furnace 

 and the phosphorus distilled over into a glass receiver. The 

 finely painted figure of the alchemist with the furnace and 

 receiver constitutes the principal feature of the picture. The 

 end of the retort protrudes from the furnace, and the spherical 

 receiver which was called a balloon is luted to the retort. The 

 balloon is nearly half filled with water and, as the phosphorus 

 distils over, the upper part is filled with luminous vapour, 

 whilst from the small hole in the top near the neck of the 

 balloon the vapour rises in a luminous jet. The balloon with 



