298 ANNUAL REPORTS OF DEPARTMENT OF AGRICULTURE. 



for the hiireaii to pursue these investigations to the point where 

 commercial success is finally assured without additional funds. 



Numerous pi-ohlems have arisen in connection with these investi- 

 pitions which liax'c broadened their scope considerahl}'; for instance, 

 the practical)ility of usin<!; other types of furnaces; the use of various 

 kinds of fuel : the best methods of furnacing the different classes 

 of phosphate rock; the purification of the phosphoric acid obtained 

 and the most economical form in which to market this acid; the 

 collection of fluorine compounds evolved in the process and the prac- 

 ticability of i-enderino; the slag obtained of marketable value. 



The phosjihate work, therefore, requires not only a much enlarged 

 personnel but considerable ecjuipment of a costh- natuiv. and a(k'- 

 (juate i)rovision should be made for the study of this broad problem 

 of utilizing to the best advantage our resources of phosphates and 

 phosphate minerals in a separate item in appropriating for the Avork 

 of the bureau. 



POTASH FROM CEMENT PLANTS AND BLAST FURNACES. 



In previous reports reference has been made to Avork carried on 

 by the bureau on the recoA^ery of potash from silicate rocks. As a 

 result of these iuA^estigations it was concluded that the most promis- 

 ing methods for recovering potash from this source consists either 

 in igniting the rock Avith limestone as in the manufacture of cement. 

 or in digesting the rock with free lime and water under pressure. 

 In the first process, the potash is volatilized and passes from the 

 kilns in the process of burning, Avhile in the second it passes into 

 solution during the digestion. In both cases the residue is suited 

 for the manufacture of cement or other building material. At the 

 present time these tAvo processes are both being developed on an 

 industrial scale, and of the numerous methods that have been tested 

 out during the Avar these alone are the only ones, so far as knoAvn. 

 that are noAV being operated commercially for the extraction «>f 

 potash from silicate rocks. This result would thus seem to justify 

 the conclusion reached by the bureau as an outcome of the investiga- 

 tions made. 



In a survey that Avas made of the cement industry by this bureau 

 it vjas found that the total potash that escapes from all the plants 

 of the countrA', as at present operated, amounts to about 87,000 tons 

 of K/J. Separate estimates Avere also made of the potash that escapes 

 from each individual plant. Installations have since been placed in 

 a number of these plants for the recovery of potash, and in cA-ery 

 case the quantity that was found to escape from the kilns checked in 

 a remarkable Avay Avith the estimates that have been made by this 

 bureau. There is, therefore, every reason to assume the reasonable 

 correctness of the total estimate made for all the plants of the 

 country. 



The"^total potash collected from cement plants in 1917 amounted to 

 1.621 tons, but in 1919 the production Avas only 1,250, or about 1 per 

 cent of the total that is lost in this industry. The decrease in the 

 production in 1919 was due to unforeseen difficulties which deA^eloped 

 in the collection of the potash and in preparing it in a marketable 

 condition. It was found, for instance, that the percentage of potash 



