Dr. Gibbs on the Determination of Nitrogen by Weight, 537 



face of the water in other directions. Thus, if currents be set up 

 outward from a point in the direction of the straight arrows, 

 there will be an indraw to the point as shown by the curved 

 arrows. The surface water being driven away in two directions, 

 other surface water must flow in to supply its place. Some- 

 times the powder rotates in complete circles or eddies. In such 

 a case it is constantly tending to sink in the lower water by 

 the side of a current which tends to carry it forward. These are 

 precisely the conditions necessary to the formation of an eddy. 



King's College, London, 

 May 5, 1864. 



LXXVIII. On the Determination of Nitrogen by Weight, By 

 Wolcott Gibbs, M,D. 3 Rumford Professor in Harvard Univer- 

 sity *. 



BUNSENf has given a method of analyzing nitrates and 

 nitrites which renders it possible to determine all the con- 

 stituents of the salt in a single analysis. This method consists 

 essentially in igniting the salt in an atmosphere of nitrogen gas, 

 absorbing the oxygen evolved by metallic copper, and collecting 

 the water in a chloride-of-calcium tube. The nitrogen in the 

 salt is given by the loss of weight in the apparatus. 



In those analyses of nitrates or nitrites in which it is only 

 desired to determine the nitrogen, the following process may be 

 employed with advantage. A hard glass tube, about 6 inches 

 in length, is sealed at one end, and its volume determined by 

 filling it with mercury and pouring this into a graduated vessel. 

 The tube is to be carefully dried and weighed with a good cork ; 

 it is then to be filled with finely-divided metallic copper, pre- 

 pared by reduction of the oxide, so as to enable the operator to 

 judge of the quantity necessary. The salt to be analyzed is 

 then weighed and mixed with the metallic copper, either in a 

 mortar or with a mixing wire in the tube, and the tube with its 

 contents and cork is again weighed. The weight of the copper 

 employed is thus known, and its volume may then be found by 

 dividing this weight by the density of metallic copper. A 

 weighed chloride-of-calcium tube is then adjusted as in organic 

 analysis, and the combustion-tube is heated in the usual manner. 

 When the combustion is finished, the open end of the chloride- 

 of-calcium tube is sealed with the blowpipe flame and the com- 

 bustion-tube allowed to become perfectly cold. The chloride 

 tube is then removed and weighed, and the combustion-tube 



* From Silliman's American Journal for May 18G4. 

 t Ann, der Chem. und Pharm. vol. lxxii. "p. 40. 



