January 14, 1887.] 



SCIENCE. 



39 



whole is not enriched by this process, the surface 

 soil is, and this concentration of nitrogen in a 

 smaller soil area may greatly facilitate the growth 

 of a succeeding shallow-rooting and quick-grow- 

 ing crop. Drechsler * has attempted to show that 

 such an enrichment of the surface soil is impos- 

 sible. He argues, that, since the roots develop 

 chiefly where they find food, if they find their 

 supply of nitrogen chiefly in the subsoil, they will 

 develop chiefly there, and consequently will not 

 enrich the surface soil. It is not diflicult to 

 show, however, that this reasoning is fallacious. 

 It is no more difficult to conceive that nitrogen 

 should be transferred from the subsoil roots to 

 the surface-soil roots, if the latter found an 

 abundant supply of mineral matters at hand, 

 than it is to conceive that both nitrogen and 

 ash ingredients may be transferred from the 

 roots to the aerial parts of the plant, provided 

 the latter find a suflicient supply of carbon di- 

 oxide. Let us suppose the surface soil to be 

 absolutely destitute of nitrogen to the depth of 

 six inches, and that the nitrogen of the seed is 

 sufficient to supply the growth of a root down 

 into the nitrogen-bearing layers below. A plant 

 would certainly grow under such conditions ; and, 

 when the crop was harvested, its stubble and what 

 roots it had formed in the upper six inches of the 

 soil would contain nitrogen, and the surface soil 

 would be enriched to just this extent at the ex- 

 pense of the subsoil. 



It would appear, then, that such an enrichment 

 of the surface soil is possible. But few experi- 

 ments calculated to demonstrate its actual occur- 

 rence have been made. The problem is not an 

 easy one. It is difficult to take samples of a soil 

 which shall be truly average samples ; and the 

 percentage differences are so small that they 

 may easily be hidden by an error in sampling. 

 Analyses by Deherain and by Lawes and Gilbert, 

 however, appear to show that such a gain does 

 take place. 



Finally, the relative power of different plants 

 to assimilate nitrogen has an important bearing on 

 this question. Wagner has rendered it probable 

 that leguminous plants are able to assimilate 

 freely the comparatively insoluble nitrogen of 

 the soil, while the cereals require their nitrogen 

 in an easily soluble form. If this is true, one of 

 the functions of enriching crops may be assumed to 

 be to gather the nitrogen of the soil which is un- 

 available to other crops, concentrate it in its roots 

 and stubble, and yield it up again by decay to the 

 following crop. 



On the whole, it does not seem difficult to ac- 

 count for the effects of enriching crops without 

 1 Journ. f. landw, xxxi. 30. 



supposing that they draw materially from the ni- 

 trogen of the air, while not excluding the possi- 

 bility of their so doing. Whether our agriculture 

 is flourishing, as Lawes and Gilbert mainlain, at 

 the expense of the accumulated nitrogen of past 

 centuries, or whether there are processes by which 

 free nitrogen is brought into combination again in 

 quantities sufficient to balance the evolution of 

 free nitrogen which we know to be continually 

 going on, is as yet an unsettled question. 



H. P. Aemsby. 



NATURAL GAS. 



A LECTURE on the subject of natural gas was 

 delivered at the Franklin institute on Saturday 

 evening, Dec. 18 last, by Mr. Charles A. Ash- 

 burner, geologist in charge of the State geological 

 survey. The lecturer stated that natural gas was 

 by no means a recent discovery. Even its utiliza- 

 tion for the purposes of the mechanic arts had 

 been successfully attempted in China, where, by 

 pipes of bamboo, it had been conveyed from nat- 

 ural wells to suitable furnaces, where, by means 

 of terra-cotta burners, it was consumed. In the 

 confines of Persia, in the south of France, and in 

 our own western states, burning-springs had long 

 been known. When Lafayette visited this coun- 

 try in 1831, the inn in the town of Fredonia, N. Y., 

 was illuminated in his honor by gas procured 

 from a neighboring well. It is, however, only 

 within recent years that natural gas has arisen to 

 any importance in its bearing on the mechanic 

 arts. At present the great iron and glass works 

 of Pittsburg and of other places are supplied with 

 natural gas as their only fuel, and millions of 

 cubic feet are yearly consumed in Pittsburg and 

 similarly situated cities. 



Of the origin of natural gas there seems to be 

 no reasonable doubt. It arises from the decompo- 

 sition of forms of animal or vegetable life embed- 

 ded in the rocks in suitable situations. The gas 

 is not believed to be generated continuously, but 

 merely to be stored in porous or cavernous rocks 

 overlaid by impervious strata. When these col- 

 lections are tapped, the gas is set free, but a new 

 supply is not being formed to take its place. The 

 position at which the gas is found is very vari- 

 able, depending upon the force of gravity and 

 upon the position of the porous layer in which the 

 gas is confined. The lecturer entered into an ac- 

 curate description of the localities in which the 

 gas was found, and gave the reasons why it was 

 hopeless, from geological grounds, to look for nat- 

 ural gas east of the Alleghenies. The region in 

 which the gas is found is practically embraced in 

 that portion of Pennsylvania west of the AUe- 



