A connection between Servian and Roumanian railways is to be established by bridging the Danube. It is reported proposals have already been made to the governments interested, by the Union Bridge Company, also by British and French constructors.—Uhland's Wochenschrift.
LIQUID RHEOSTATS.
By H. S. Webb.[1]
The object in view when the following tests were commenced was to obtain some data from which the dimensions of a liquid rheostat for the dissipation as heat of a given amount of energy could be calculated, or at least estimated, when the maximum current and E.M.F. are known. These tests were rather hastily made and are far from being as complete as I should like to have them, and are published only to answer some inquiries for information on the subject.
In the first test, an ordinary Daniell jar (6¼ inches in diameter by 8 inches deep) with horizontal sheet iron electrodes was filled with tap water. It would not carry 4 amperes for over fifteen or twenty minutes, although the jar was full of water and the plates only ¾ inch apart. After that length of time it became too hot, causing great variation in the current on account of the large amount of gas liberated, much of which adhered to the under surface of the upper electrode. The difference of potential between the plates was 200 volts.
A run was made with 1 ampere and then with 2 amperes for one hour. In the latter case the voltage between the electrodes was about 71 volts and the temperature rose to about 167° F.
From these tests it would be safe to allow a vessel with a cross section of 30.7 square inches to carry from 2 to 2½ amperes when tap water and horizontal electrodes are used.
In test No. 2 the same jar and electrodes were used as in the preceding test, but the tap water was replaced by a saturated solution of salt water. Eleven amperes with a potential difference of 7 volts between the electrodes, which were 7¾ inches apart, were passed through the solution for three hours, and the temperature at the end of the run was 122° F., and was rising very slowly.
Although the current per square inch is much greater, the watts absorbed per cubic inch is much less in this case than when water was used. With the water carrying 2 amperes the watts absorbed would be over 10 per cubic inch, while for the saturated solution of salt when carrying 11 amperes it would be only about 0.4 watt.