4 PROCEEDINGS OF THE AMERICAN ACADEMY 



employment of much larger quantities of salt for analysis. On the 

 other hand, it presents another difficulty, arising from the fact that the 

 dry mercurous tungstate adheres with excessive tenacity to the evapo- 

 rating vessels, whether of glass, porcelain, or platinum, so that the first 

 method is on the whole to be preferred. 



The separation of tungstic oxide from other bases is best effected 

 by fusing the salt with an excess of potassio-sodic carbonate and dis- 

 solving out the alkaline tungstates formed. 



Normal sodic tungstate has long been known, and all the analyses 

 concur in assigning to it the formula 



W0 4 Na 2 + 2 aq. 



It is now to be had from various German firms in a state of purity, 

 and forms the most convenient material for the study of the com- 

 pounds of tungsten. The acid salt analyzed by Anthon, and to which 

 the formula 



W 2 O r Na 2 -4- 4 aq 



was long ascribed, is now well known to have an entirely different 

 composition ; but Lefort* has recently endeavored to show that ditung- 

 states and tritungstates really exist, and has described a number of salts 

 of each series. Lefort obtains sodic ditungstate by adding glacial 

 acetic acid to a saturated solution of the neutral salt until the reac- 

 tion with litmus becomes acid. After a day or two the salt separates 

 in long prismatic crystals, with the formula 



W 2 7 Na 2 -f 6 aq. 



I have repeatedly attempted to prepare the ditungstate by this 

 process, but without success in any one instance, the resulting salts 

 being, as I shall show further on, in all cases very different in compo- 

 sition. Lefort prepared sodic tritungstate by pouring a concentrated 

 solution of the ditungstate into a boiling solution of glacial acetic acid. 

 His analyses agree fairly well with his formulas, and I have adopted 

 his results without question, in the belief that my own inability to 

 reproduce them was due to the omission in his paper of some matter 

 of detail which appeared insignificant, but which was really important. 



Ten to Four Sodium Salt. — The salt to which I have given this 

 name appears to have been first observed by Forcher,f who obtained 



* Ann. de Chimie et de Physique, (5,) ix. 93. 

 t Wiener Akad. Berichte, xliv. 2, 177. 



