1 84 PROGRESS OF SCIENCE. 



of which contain equal numbers of elementary atoms > similarly 

 arranged, have the same crystalline form" which has been 

 slightly modified, but which nevertheless was a powerful 

 assistance in Berzelius's researches in atomic weights. 



1800 69. Dumas invented the method of determining 

 the DENSITIES OF COMPOUNDS in the gaseous state, known as 

 Dumas's vapour density process; established the relations 

 which exist between ethers and alcohols, and between ethers 

 and acids ; determined the composition of chloral and chloro- 

 form ; formulated the UNITARY THEORY, in opposition to 

 Berzelius's dualism, by which it is conceived that "the mole- 

 cule of a compound is regarded as a unitary structure " ; 

 originated the conception of types developed by Gerhardt and 

 Laurent. 



18031873. Liebig, one of the greatest masters of OR- 

 GANIC CHEMISTRY (so called) ; was more successful than any 

 in applying chemistry to PHYSIOLOGY, PATHOLOGY, and 

 AGRICULTURE. His agricultural chemistry has rendered 

 immense service to Europe and America ; he taught that the 

 chemical state of the soil affected plants in many ways 

 hence crops and animals ; and showed how important it was 

 to preserve the vitality of the soil by sowing it with proper 

 seeds, and how to improve fields by certain processes and 

 manures. Regarding physiology, Liebig was equally scien- 

 tific and practical ; he showed the changes which food under- 

 goes in our bodies, and what part becomes blood, what part 

 fat, or bone, or muscle demonstrating that the body of 

 animals is a chemical laboratory always at work, producing, 

 combining, decomposing substances. He improved manipu- 

 lation by several innovations: his POTASH-BULBS made an 

 organic analysis one of the simplest operations of chemistry, 

 and the process (since 1831) caused rapid advances to be 

 made. He may be said to have changed the whole face of 

 that branch. Invented a condenser for distilling small 

 quantities of liquids. He produced chloroform and chloral 

 (1832), benzoyl, and contributed to establish Dumas's unitary 

 theory. His Letters on Chemistry aroused universal interest 

 in the science. 



18051869. Graham (Thomas) discovered the LAW OF 



