262 ANNUAL OP SCIENTIFIC DISCOVERY. 



baryta), coal-tar, and sawdust. Each molecule of the carbonate being- thus 

 brought in contact with the reducing agent, carbon, excellent results are 

 obtained, the decomposition of the carbonate being easy, and the product of 

 baryta abundant. (It was from observing the odor of ammonia, Avhich was 

 at times developed during their experiments upon this method of preparing 

 baryta, that the authors were led to the discovery in question.) "\Vhcn the 

 baryta thus obtained is calcined in the presence of charcoal and atmospheric 

 air, it combines readily with carbon and the nitrogen of the air, and a forma- 

 tion of cyanide of barium and carbonic oxide results. This product of 

 cyanide of barium is then received into an iron cylinder, through which a 

 current of steam at a temperature of about five hundred and seventy-two 

 degi-ees Fahrenheit is passed, and under these circumstances the cyanide of 

 barium disengages in the form of ammonia all the nitrogen which it contains. 

 Trials made by the discoverers of this process, upon a tolerably large scale, 

 are reported to have been eminently successful, leading them to hope that 

 not only the various cyanides employed in the arts, but also ammonia and 

 nitric acid, may thus be economically produced. 



ON THE SOURCES OF NITROGEN IN PLANTS. BY DR. CHARLES 



CAMERON, F. R. C. 



Previous to the year 1857, our knowledge of the sources of the most impor- 

 tant (agronomically considered) of the organic constituents of the food of 

 plants, nitrogen, was limited to the following substances : 



Ammonia and its salts. 



The nitrates of the alkalies. 



The cyanides of potassium and sodium. 



These substances have been proved, beyond all doubt, to be capable of 

 furnishing nitrogen in plants; but there are other bodies whose capability of 

 supplying this element to vegetables is still a qucestio vexala. These bodies 

 are free nitrogen, that gas which forms the most abundant constituent of 

 the atmosphere, and the nitrogenous organic matter termed huimfs (the 

 altered remains of plants), a substance which is present in every fertile soil. 



There are, I believe, but few vegetable physiologists who now insist that 

 plants are capable of assimilating uncombined nitrogen; but many of the 

 most celebrated investigators of phyto-chemistry, whilst admitting that 

 plants derive a large proportion of their nitrogen from the ammonia of the 

 atmosphere and the soil, maintain that the greater proportion is furnished to 

 them by the soluble organic matter of the soil. For my own part, I have 

 satisfied myself, by numerous carefully conducted experiments, that neither 

 the free nitrogen of the atmosphere nor the combined nitrogen of humus 

 can be assimilated by plants. I have further satisfied myself that the nutri- 

 ment of plants can only be supplied by substances of a purely inorganic 

 nature, under which designation I include a considerable number of sub- 

 stances such as ammonia and urea which are commonly, though I 

 believe incorrectly, considered as pertaining to the organic kingdom. Some 

 of the results of my researches in this domain of science have been published 

 in various journals since 18-37. These researches prove that the sources of 

 the nitrogen of plants are not limited to the substances above enumerated; 

 but that, in addition to these, urea and the cyanurates of potash and soda, 

 compounds exceedingly rich in nitrogen, are capable of yielding that element 

 to growing plants. Since the publication of these experimental results, I have 



