60 PROCEEDINGS OF THE AMERICAN ACADEMY. 



The foregoing table contains a summary of all the experiments, 

 reduced to a common basis. Thus the column headed ' k Dull Red- 

 ness " shows that on the average baric chloride ignited at about 500° 

 or 600° loses three parts in one hundred thousand of its weight. The 

 true weight of the baric chloride was computed in each case by add- 

 ing the alkalimetric correction to the last weight taken ; and then 

 the percentage of excess or deficiency in weight was computed for 

 each temperature and tabulated in its appropriate place. 



The variations noticeable in the amounts of water retained at the 

 lower temperatures are probably in great part due to the varying 

 hygroscopic condition of the atmosphere at the time of drying, as 

 well as to inaccuracies in the temperatures recorded. 



There are necessarily three standards for determining the true 

 weights of baric chloride forming the basis of the tahle above : one 

 involves the weight of the salt ignited at dull redness plus the alkali- 

 metric correction (Experiments 1, 2, 3, 4, 5, 6, 9, and 10) ; another 

 involves the weight of the salt ignited at bright redness plus the same 

 correction (Experiments 7, 8, and 11); and the third involves the 

 weight of the salt fused in hydrochloric acid, without any correction 

 (Experiments 12, 13, 14, and 15). A comparison of the results of 

 Experiments 11, 13, and 15 with all the earlier experiments is suffi- 

 cient to show that the three standards are very nearly, if not quite, 

 identical ; in other words, that baric chloride which has been dried at 

 dull redness, or even at 400°, does not lose an essential amount of 

 water upon being heated nearly to 900°. Nevertheless, below 400° — 

 which is about the point at which the salt begins to show signs of 

 partial decomposition — very noticeable amounts of water appear to 

 be held by the so called anhydrous salt. 



The conclusion regarding the expulsion of water from the baric 

 chloride is so important that it seemed desirable to prove it in another 

 way. Hence two determinations of the water of crystallization of 

 perfectly homogeneous powdered pure baric chloride were made by 

 two distinct methods : — 



(16.) In the first case 3.10784 grams (in vacuum) of the powdered 

 crystals were dried at a medium red heat by means of a spirit lamp to the 

 constant weight of 2.64851 grams (in vacuum) and cooled in a vacuum 

 over phosphoric anhydride. The solution of this salt required 1.00 c.c. 

 of standard hydrochloric acid (of which the cubic centimeter corresponded 

 to a milligram of silver) to render it neutral to phenol phthalein, and 

 0.85 c.c. more to reach the neutral point with regard to methyl orange. 



