

Gooch and Kuzirian — Use of Sodittm Paratungstate. 497 



Art. XLI. — The Use of Sodium Paratungstate in the Deter- 

 mination of Carbon Dioxide in Carbonates and Nitrogen 

 Pentoxide in Nitrates by Loss on Ignition • by F. A. Gooch 

 and S. B. Kuzirian. 



[Contributions from the Kent Chemical Laboratory of Yale Univ. — ccxx.] 



From certain carbonates, like those of magnesium, zinc and 

 cadmium, carbon dioxide may be expelled by simple ignition 

 at a moderate temperature, leaving an oxide in definite and 

 weighable condition. In the case of calcium carbonate, this 

 process of decomposition is completed only at the high heat 

 of the blast lamp, and the reaction, being easily reversible in 

 the atmosphere containing carbon dioxide evolved in the igni- 

 tion or produced in the source of heat, may leave the oxide not 

 quite pure. Strontium carbonate and barium carbonate are 

 not entirely broken up by simple ignition under the conditions 

 ordinarily available in analysis ; nor are the alkali carbonates. 

 For the decomposition of refractory carbonates it is customary 

 to make use of a suitable flux which, by combining with the 

 oxide, will aid in the expulsion of the carbon dioxide. Anhy- 

 drous borax,* silicon dioxide, f potassium dichromate,^: and 

 recently, sodium metaphosphate§ have been thus used in the 

 analysis of carbonates, and they are applicable similarly to the 

 determination of nitrogen pentoxide in nitrates which leave 

 definite oxides on ignition. Such fluxes, moreover, serve the 

 very essential end of conserving the residual oxides in definite 

 and stable form for weighing under the ordinary atmospheric 

 condition of the balance room. Of those mentioned the first 

 two, borax and silicon dioxide, require prolonged ignition to 

 bring them to constant weight before making use of them to 

 react with the carbonate or nitrate ; and generally they yield in 

 the fusion process a pasty magma, so that prolonged heat at a 

 high temperature is necessary to the complete expulsion of the 

 gaseous product. Sodium metaphosphate, though more fluid 

 in fusion, also demands prolonged care in the preparation. 

 Potassium dichromate is too easily decomposed with loss of 

 oxygen to be employed in exact processes demanding long con- 

 tinued fusion or heating to temperatures much above its fusing 

 point. 



These are points which have been sufficiently emphasized in 

 the work to which reference has been made. 



*Fresenius : Zeitschr. anal. Chein., i, 181. 



\ Eose : Ann. Pays., cxri, 635. Presenilis: Zeitschr. anal. Chem., i, 184. 

 Eichards and Archibald, Proc. Am. Acad., xxxviii, 443. 



% Eose : Ann. Phys., cxvi, 131. Fresenins : Zeitschr. anal. Chem., i, 183. 



j? Lutz and Tschischikof : Chem. Zentralblatt, 1905, i, 564. Bottger : 

 Zeitschr. anal Chem., xlix, 487. 



