186 HYDRATES IN AQUEOUS SOLUTION. 



EXPERIMENTAL FACTS AND DATA. 



In the succeeding pages the experimental material will be presented in 

 the following order: All the facts obtained by spectrographic means, per- 

 taining to the simple aqueous solutions containing cobalt chloride, will 

 be given first; then those relating to cupric chloride, and finally those per- 

 taining to cupric bromide. Following this, the solutions obtained by adding 

 either calcium chloride, or calcium bromide, or aluminium chloride, to the 

 simple aqueous solutions, will be taken up in the order in which the dehy- 

 drating agents have been named. For any set of solutions, the data obtained 

 by the photographic method will appear immediately after the record of 

 the concentrations. The results of eye observations with the spectroscope 

 will then be presented, and following this the freezing-point lowering will 

 be given. Conductivity data (expressed in reciprocal ohms and reciprocal 

 centimeters) will then be presented, and, finally, attention will be called to 

 any other facts that have been noted. 



SOLUTIONS. 



The aqueous solutions investigated were made up as follows: A chosen 

 volume of the mother-solution of a colored salt was measured out from a 

 burette into a measuring flask of known capacity. The portion of solu- 

 tion in the flask was then diluted by the addition of pure* water, until the 

 volume of the resulting homogeneous liquid was exactly equal to the fixed 

 capacity of the flask. The same flask was used in making up all the solu- 

 tions studied throughout the entire investigation. The concentrations 

 will always be expressed as multiples of normal. The term normal will 

 be used exclusively to mean gram-molecular normal, i. e., a liter of solu- 

 tion which contains just as many grams of anhydrous salt as there are 

 units in the number expressing the molecular weight of the salt, is defined 

 as normal. Hence, if a liquid is composed of wf gram-molecules of salt in a 

 liter of solution, its concentration is n times normal. In general, several 

 solutions of one set were made up with reference to their colors; in other 

 words, in such a manner as to employ as wide a range of concentrations as 

 could be conveniently photographed, and at the same time to bring out 

 the delicate changes in tint, by having the successive differences in con- 

 centration as small as desirable. 



When a solution contained both a colored salt and a colorless dehydrat- 

 ing agent, it was mixed as follows: A certain known volume of the mother- 



*This water had been distilled several times, so that its conductivity was as low as 

 1.1 X 10~ 7 at C. on the average. 



|n can have any positive value, integral or fractional. , ,. 



