260 S. W. Johnson — Estimation of Nitrogen in Nitrates. 



We take pleasure in dedicating this elegant species to Count 

 L. F. de Pourtales, the eminent Zoologist of the Museum of 

 Comparative Zoology at Cambridge, Massachusetts, who first 

 called attention to the relations of this genus to one of the types 

 of recent Crinoids. 



Geological position and locality : from the lower part of the 

 Lower Burlington Limestone, Burlington, Iowa. Collection of 

 Frank Springer. 



Art. XXIX.— On Thorpe's and Bunsens methods for the Esti- 

 mation ':>■ .- by S. W. Johnson.— • 

 tionsfrom the Sheffield Laboratory of Yale College. No. XL VI. 



In volume xxvi, pp. 541, 549, of the Journal of the Chemical 

 Society, as well as in his treatise on Quantitative Analysis, p. 95, 

 Thorpe has described a method of estimating nitric acid, in 

 which this acid is reduced to ammonia by the use of slips of 

 zinc coated with, precipitated copper, a reduciug combination 

 first employed by Gladstone and Tribe. The experimental re- 

 sults given by Thorpe in support of his method are such as 

 apparently establish its great exactness, while in s 

 and ease of execution, it would seem to be quite superior to 

 the similar methods that have been previously proposed. 



Having occasion to make some determinations of nitric acid, 

 I tested Thorpe's method in five distinct trials with pure sodium 

 and potassium nitrates. The directions given by Thorpe in 

 his Quantitative Chemical Analysis are as follows: 



About 25-30 grams of thin sheet zinc are placed in a flask of 

 about 200 c. c. capacity, and covered with a moderately con- 

 centrated and slightly warmed solution of copper sulphate. In 

 about ten minutes a thick spongy coating of copper will be de- 

 posited on the zinc ; the liquid is poured off the metal 

 are now well washed with cold water and covered with about 

 40-50 c. c. of pure water. Weigh out about 0*5 gram of 

 pure nitre into the flask connected with a condensing arrange- 

 ment The liquid is gradually heated and distilled for about 

 an hour. The distillate is treated with platinum tetra 



These directions were followed as closely as possible save 

 that the distillate was received in a standard acid in order to 

 measure the ammonia volumetrically. 



In the first experiment 0"5712 of sodium nitrate were em- 

 ployed, containing 0-09408 of nitrogen. After distillation was 

 concluded, the distillate contained 0*02947 of nitrogen. Think- 

 ing that the zinc hydroxide resulting from reduction of the 

 nitrate might retain ammonia beyond the power of simple dis- 



