52 THE UNITED STATES GEOLOGICAL SURVEY. [hill. 227. 
variety and sometimes of doubtful accuracy. In several cases the Sur- 
vey has been called upon to standardize work of this kind. Some years 
ago, at the request of the Colorado Scientific Society, a uniform sample 
of ore containing zinc was prepared. One portion of this was sent to 
the Survey laboratory, and other portions were distributed to a number 
of chemists in Colorado. The latter determined their zinc by a variet} 7 
of rapid methods; the Survey sample was analyzed with the utmost 
care and accuracy. In this way it was determined which of the rapid 
methods was the best, and the smelter chemists of Colorado were aided 
in their work. In a similar manner the Survey has formulated the 
best method for the proximate analysis of coal, and recentlj 7 there has 
been made a very thorough investigation of the analysis of Portland 
cement. In the latter case the work was initiated by the New York 
section of the Society for Chemical Industry. Uniform samples of 
cement rock and finished cement were prepared and distributed among ' 
about 20 different chemists who were engaged in that class of work. 
The Survey analyses served as a standard by which to check others, 
and the result is a decided improvement in this class of technical work. 
Another field of labor which has been much cultivated by the chem- 
ists of the Survey is that of purely scientific research. At present 
investigations are under way having for their purpose the elucidation 
of the processes which operate in the secondary enrichment of ore 
bodies. Elaborate investigations have also been made and are still in 
progress relative to the chemical constitution of the natural silicates, 
and these have shed much light on the troublesome question of molec- 
ular structure. It has been found, for instance, that various silicates 
are easily broken up by heat alone in such way that the changes occur- 
ring can be measured quantitatively. Thus, talc on ignition has one- 
fourth of its silica split off in the free state. Other minerals break 
up into two portions, one soluble and the other insoluble in strong 
acids, and in the case of the chlorites the insoluble portion has the 
composition of spinel. It has also been found possible to effect 
replacements in silicates analogous to those which the organic chemist 
employs in determining the structure of a hydrocarbon, and one group 
of silicates has thus been prepared in which the bases, soda, lime, and 
potash, have been replaced by the compound radical ammonium. Sili- 
cates containing 10 per cent of ammonia have been prepared which 
were perfectly stable at 300° C. These are the first ammonium silicates 
known to science. The chief chemist has also been called upon to act 
as chairman of the International Commission on Atomic Weights. 
Other investigations have had practical aims in view. The elaborate 
research undertaken by one of the chemists on natural soda is a case in 
point. The alkaline lakes of California, Owens and Mono lakes par- 
ticularly, contain large quantities of sodium carbonate, and the prob- 
lem in hand was to determine the conditions under which that salt 
