10 BULLETIN 102, PABT 2 , UNITED STATES NATIONAL MUSEUM. 
attention to the sulphur deposits of Louisiana and Texas as a possible 
source of raw material, although these deposits, while cheaply 
worked, have been thus far shipped for other uses owing to the 
purity of their product. 
The fate upon return of normal conditions of the numerous small 
activities that have developed to tide over the present pyrite shortage 
should merit the serious attention of the United States ; for resump- 
tion of conditions that delayed the development of these domestic 
activities will cause their decadence. Moreover, the failure of the 
Government to formulate a definite policy in regard to just such 
post-war conditions has evidently retarded the industrial efforts 
needed as a remedy for current conditions. 
Nitrogen. 
It is not intended to indicate the relative importance of the three 
major plant foods by the order in which they are taken up here: 
their functions, indeed, are different, and they are consequently not 
open to comparison in this respect. Nitrogen, however, is the ele- 
ment customarily cited first on the labels of commercial fertilizers, 
and it may conveniently be taken up next. Nitrogen, of course, does 
not appear in fertilizers in the elemental or gaseous condition, but 
in the form of various chemical compounds, such as sodium nitrate 
(also called Chile saltpeter, or merely nitrate), ammonia, ammonium 
sulphate, and complex organic compounds; all, in short, more or 
less soluble in the weak acids which operate around the roots of 
plants and convey the plant food in solution to its destination. 
Nitrogen contributes stalk growth to the plant. When it finds its 
wa}^ to the bodies of animals it enters into the composition of the 
proteid compounds, which are present in every cell, playing a part 
of essential importance in the life processes. Unlike phosphorus 
and potassium, nitrogen is not a product furnished by the weather- 
ing of rocks, but its source is the atmosphere, which, indeed, is com- 
posed to the extent of about 78 per cent of this gas. But so long as 
neither plants nor animals are adapted for breathing in the required 
nitrogen direct, a roundabout method has been evolved whereby 
microscopic organisms known as bacteria, present on the roots of 
plants, transform the atmospheric nitrogen into compounds of suit- 
able nature for assimilation. A class of plants, the legumes, of 
which clover is a familiar example, has the ability of fixating nitro- 
gen in this way to an unusual degree; and a crop or so of such 
plants, when turned back into the soil, form a common expedient 
for increasing the nitrogen content of farm land. 
The most prominent source of nitrogen has long been sodium 
nitrate, a natural salt occurring in quantity in the deserts of northern 
Chile. It is found in the form of a thin blanket or bed which under- 
