188 Gooch and Browning — Method for the 



called by Haiiy "apotome."* The striking likeness between 

 the forms of the West Virginia celestite and the Sangerhausen 

 pseudomorphs may be seen by comparing the last three of 

 the preceding figures with those numbered 26, 31 and 32 in 

 Professor Dana's paper. This will at least serve to show the 

 resemblance which must exist between the products of the 

 locality here described and those mentioned by Haiiy near 

 Paris, where, he says, the celestite also occurs in "flattened 

 ovoid masses."! 



Art. XXY. — A Method for the Determination of Iodine in 

 Haloid Salts / by F. A. Gooch and P. E. Browning. 



(Contributions from the Kent Chemical Laboratory of Yale College. — I.) 



Few problems of analysis have been more discussed than the 

 estimation of iodine accompanying chlorine and bromine in 

 haloid salts ; and yet the constant succession of new processes 

 is sufficiently indicative that the solution of the question is not 



fenerally regarded as satisfactorily settled. The method of 

 resenius, according to which iodine is liberated by nitrous 

 acid, collected in carbon disulphide and titrated by sodium 

 thiosulphate, finds ready acceptance for the determination of 

 small amounts of iodine ; but when the quantity of iodine to 

 be estimated is considerable, the method is unwieldy. Proba- 

 bly the process most generally in use is that based upon the 

 liberation of iodine by means of a ferric salt, and the titra- 

 tion of the distillate by one or other of the well-known iodo- 

 metric methods. The latter method is fairly accurate, but the 

 requirement of special apparatus for properly condensing the 

 distillate is detrimental to rapidity and ease of execution. In 

 this process the amount of iodine set free should be measured 

 exactly by the reduction of the ferric salt, and were the ferrous 

 salt produced in the course of the action sufficiently stable, the 

 determination of its amount might be substituted for the titra- 

 tion of the iodine, and so the collection and further treat- 

 ment of the distillate might be dispensed with ; but ferrous 

 salts are too sensitive to atmospheric influence to preserve 

 under the conditions of this process their own degree of oxida- 

 tion, and the amount of iron found in the ferrous condition 

 cannot be made to serve as a trustworthy indication of the 

 reducing action which actually takes place in the separation of 

 the iodine. The advantage of replacing the collection and ex- 



* Ann. chim. et phys. Ill, vol. vii, p. 489, 1843 ; Manuel de Mineralogie, vol. iv 

 p. 119, 1874. 



f Traite, 2d ed., vol. ii, p. 37, 1822. 



