428 MEMOIR OF THE LATE DR THOMAS CHARLES HOPE. 



tlie conducting power of fluids, until the 18th January 1836, when he read, to 

 the Royal Society of Edinburgh, the first part of a paper entitled, "Observations and 

 Ea^perhnents on the coloured and colourable matters in leaves and flowers of plants, upmi 

 which acids and alkalies act in p'oducing red, yellow, or green colours." A second 

 part of this paper was laid before the Society on the 21st of the following March. 



Although chemists have at all times used coloured vegetable infusions for 

 indicating the presence of acids and alkalies, no researches appeared to have been 

 made on the peculiar vegetable principle on which the acid and alkali acted ; and it 

 was generally taken for granted that both descriptions of agents acted on one and the 

 same principle. Dr Hope endeavoured to shew, by various experiments on the gene- 

 ral colouring matter of plants, that vegetable infusions, which became red by the 

 addition of an acid, and green or yellow by an alkali, contained two distinct prin- 

 ciples, on one of which acids acted, and alkalies on the other. To the former he 

 proposed the name otErythrogene, and for the latter that of Xanthngene. Decan- 

 DOLLE had distinguished the colouring matter of flowers by the name of Cliromule ; 

 and Ellis speaks of the substance which may become green, red, or yellow, under 

 diflerent circumstances, as the colourable matter of plants. The object of Dr PIope's 

 researches was to prove, that this matter was not an individual substance, but 

 consisted of two distinct vegetable principles, which exist either separate or com- 

 bined in different plants. He illustrated this by many experiments on different 

 sorts of plants, and gave the results in eight tables. He shewed that all green 

 leaves, all white and yellow flowers, contain only one of these principles, viz., 

 Xanthogene, that all red and blue flowers, also all leaves with red colours, contain 

 both Xanthogene and Erytlrrogene (with the single exception of Litmus, which 

 contains no Xanthogene), and that red flowers abound in Erythrogene. The 

 distinct nature of these proximate principles of vegetables he infeiTed from the 

 different modes in which they are affected by chemical re-agents. 



In the same year Dr Hope made a communication to the Society " On the 

 Chemical Nomenclature of Inorganic Compounds.'''' He pointed out the disadvan- 

 tages of the want of a discriminating and uniform nomenclature among teachers 

 and writers on chemistry ; and stated certain changes which he had for some 

 time employed in his lectures. 



The changes proposed were — 



1. To discard the prefixes piroto, per, super, sub, for compounds. 



2. To adopt rigidly the happy suggestion of Dr Thomson, viz., to employ the 

 Greek numerals to denote the number of atoms or equivalents of the base of a 

 compound, and the Latin numerals for the number of atoms of the oxygene 

 or acid. 



3. To avoid as much as possible the intermixture of Greek and Latin in 

 numerical indications. 



