Manchester Memoirs, V^ol. xlvii. (1902), No. V*. 13 



glass. When more dilute solutions of baryta water were 

 employed, the action on powdered glass was distinct, but 

 this has no bearing on the Pettenkofer test. Solutions of 

 all three alkaline earths acted on silica, lime to the 

 greatest extent and baryta least, strontia, as in so many 

 of its reactions, standing mid-way between lime and 

 baryta. 



It may be objected that the preceding experiments, 

 carried on in bottles of small capacity, cannot be fairly com- 

 pared with those carried on in the large bottles required 

 for the Pettenkofer test. To settle this point the following 

 experiment was made. Baryta water was placed in a large 

 bottle (A), Fig. 2, such as is commonly, used for the test, 

 it was closed with a doubly bored india rubber stopper, 

 through which passed two tubes, one leading below to the 

 baryta water (the upper end being closed with a cap), and 

 the other terminating just below the stopper. This shorter 

 tube was connected by india rubber tubing with a second 

 large bottle (B) containing potash solution, and the exit 

 was connected with a U tube, also containing potash, so 

 that the air in this bottle was kept free from carbon 

 dioxide. After standing 24 hours, 10 c.c. of the baryta in 

 A were withdrawn by means of a pipette, the cap im- 

 mediately replaced and the solution titrated. The tests 

 were repeated at intervals during twenty months. When 

 started on 13th March, 1901, 10 c.c. of the baryta 

 required lyG c.c. of the half deci-normal hydrochloric 

 acid, and on October 31st, 1902, 10 c.c. of the baryta 

 required 1345 c c. of the acid, a very trifling difference 

 after such a prolonged contact. I ought to add that on 

 two occasions, for which it is difficult to account, the 

 strength diminished so that only I3"2 c.c. of the acid were 

 required, but after that it rose again, and on April 25th 

 was of the same strength as when started. The details are 

 given in the subjoined table. 



