354 HISTORY OF SCIENCE 



them yellow; it turns coloured flowers white ; it thickens oils and fats ; 

 its solution dissolves iron ; the gas attacks many metals, and combines 

 with the fixed mineral alkali (caustic soda), forming thereby common 

 salt (chloride of sodium}. A reader acquainted with the merest ele- 

 ments of chemistry will observe that Scheele had discovered chlorine. 

 But that was not the name he gave it. He was entangled in the 

 meshes of the phlogiston theory, and he supposed that the action in 

 . the retort consisted in the " black magnesia " depriving the muriatic 

 acid of its phlogiston. He gave, therefore, to the new gas the name 

 of " dephlogisticated muriatic add" The discovery of chlorine, which 

 will ever be associated with the name of Scheele, was made in 1774. 



Scheele also either first discovered the following bodies, or first 

 thought over and studied their nature and properties : arsenic acid, 

 tartaric acid, malic acid (the acid of apples), crystallized citric acid, 

 fluoric acid, lactic acid, Prussic acid, compounds of tungsten and 

 molybdenum, etc., etc. 



The great representative of English chemistry immediately after 

 Cavendish was PRIESTLEY (1733 1804), a remarkable man among 

 the many remarkable men who appeared in the latter part of the 

 eighteenth century. Joseph Priestley was born at Fieldhead, near 

 Leeds, where his father was a dresser of woollen cloth. Priestley was 

 educated at a public school, and by the time he was six years of age 

 he had made considerable progress in Latin, Greek, and Hebrew. As 

 he had always been fond of books, his friends hoped that he would 

 ultimately become a Nonconformist minister, which in fact he did. 

 Though he devoted much time to theological studies, yet by the time 

 he was twenty-three years of age he had acquired also a knowledge of 

 French, Italian, German, Chaldee, Syriac, and Arabic ; and had be- 

 sides written some religious essays. In 1755 ne was appointed as 

 assistant minister to some small chapel in Suffolk, where his income 

 did not exceed $o a year. He soon found, however, that his the- 

 ological views were not relished by his congregation, for he began to 

 deviate from the rigorous system of doctrines which the sect affected, 

 and accordingly his hearers speedily fell off. He became, too, a 

 marked victim of the odium theologicum of the ministers of other bodies, 

 and when he became a candidate for a vacant meeting-house at Shef- 

 field he was rejected. He succeeded better at Nantwich, where in 

 1758 he was appointed to a chapel, and where he increased his income 

 by keeping a school and by giving private tuition. He taught in the 

 school from seven in the morning till four in the afternoon, and gave 

 private lessons from four to seven in the evening; and yet he con- 

 trived to find time to write his English Grammar. In 1761 he suc- 

 ceeded to the office of teacher of languages in a large academy at 

 Warrington. At Warrington he married, and remained there six years, 

 and published essays on a Liberal Education, Government, Biography, 

 etc. On a visit to London he was introduced to Benjamin Franklin 



