834 THE POPULAR SCIENCE MONTHLY. 



Before taking up the investigation of the aniline dyes, Hofmann 

 had been engaged in a line of research, which, though apparently of 

 mere theoretical interest, had especially fitted him for this work, 

 namely, the study of organic ammonias, or amines. In 1849-'50 Hof- 

 mann made the discovery that when ammonia was acted upon by 

 certain alcoholic iodides, such as methyl iodide, one, two, or three of 

 the hydrogen-atoms of the ammonia could be replaced by the alco- 

 holic radical. In this way he prepared trimethylamine, a substance 

 which he subsequently found to exist ready formed in herring-pickle, 

 and from which it is still obtained for medicinal purposes. For his 

 investigations on the molecular constitution of the organic bases, he 

 was awarded the Royal Medal in 1854, and in 1887 he received the 

 great prize of the World's Fair at Paris. 



Engaged in studies of this sort, the resemblances between aniline 

 oil and ordinary ammonia, and more especially between their respective 

 salts, could not escape his notice. Each contains one atom of nitro- 

 gen ; the substitution of a certain group of atoms known as the phe- 

 nyl group for one of hydrogen will convert ammonia into aniline. 

 In the more complex molecule of rosaniline, with its three atoms of 

 nitrogen, he naturally sought for a triple ammonia, but he found the 

 phenyl group alone incompetent to form this base, which led to his 

 discovery of the very important fact that no dyes can be made from 

 pure aniline, an admixture of its homologue, toluidine, being essential 

 to the production of the rosaniline and its derivatives. 



Organic bases, containing other elements than nitrogen, have also 

 attracted his attention, and through his labors much has been added 

 to our knowledge of the " phosphines," phosphonium, etc. 



Another class of subjects, to which Hofmann has devoted much 

 attention, includes the mustard-oils, both natural and artificial, and 

 the sulpho-cyanides of organic bodies. These researches have resulted 

 in the artificial production or synthesis of many pungent oils and 

 ethers. He has also fearlessly attacked the cyanides themselves, and 

 succeeded in producing some new organic compounds that fairly rival 

 Bunsen's well-known cacodyle in their repulsive odors. 



Among the analytical processes introduced by Dr. Hofmann are 

 several of importance, including the separations of arsenic from anti- 

 mony, and of copper from cadmium, and the detection and estimation 

 of carbon disulphide. Hofmann's method of determining the specific 

 gravity of vapors is as remarkable for its simplicity as for its accu- 

 racy. 



Although a fertile writer, Professor Hofmann is not given to writing 

 books. He has, however, contributed a great many original papers to 

 various chemical journals, of which the " Journal of the London Chem- 

 ical Society " contains more than ninety, and nearly two hundred more 

 are to be found in the " Berichte " of the Berlin Chemical Society. 

 He was for a time one of the editors of Fowne's " Manual of Chemis- 



