Exhaustion Obtained With A Plain Sprengel Pump

I made a series of experiments with a plain Sprengel pump without stopcocks, and arranged, as far as possible, like the instrument just described. The leakage per hour was as follows:

 Duration of the Leakage per hour in

experiment. cubic mm. at press.

760 mm. 
22 hours 0.04563 2 days 0.04520 2 days 0.09210 4 days 0.06428 ------- Mean 0.06180

Using the same reasoning as above we obtain the following table

 Time necessary for removal Greatest attainable

of half the air. exhaustion. 
10 minutes 1 / 5,000,000 7.5 minutes 1 / 7,000,000 6.6 minutes 1 / 12,000,000

In point of fact the highest exhaustion I ever obtained with this pump was 1 / 5,000,000; from which I infer that the leakage during action is considerably greater than four times that of the pump at rest. The general run of the experiments tends to show that the leakage of a plain Sprengel pump, without stopcocks or grease, is, when in action, about 80 times as great as in the form used by me.

Note On Annealing Glass Tubes

It is quite necessary to anneal all those parts of the pump that are to be exposed to heat, otherwise they soon crack. I found by inclosing the glass in heavy iron tubes and exposing it for five hours to a temperature somewhat above that of melting zinc, and then allowing an hour or two for the cooling process, that the strong polarization figure which it displays in a polariscope was completely removed, and hence the glass annealed. A common gas-combustion furnace was used, the bends, etc, being suitably inclosed in heavy metal and heated over a common ten-fold Bunsen burner. Thus far no accident has happened to the annealed glass, even when cold drops of mercury struck in rapid succession on portions heated considerably above 100° C.

I wish, in conclusion, to express my thanks to my assistant, Dr. Ihlseng, for the labor he has expended in making the large number of computations necessarily involved in work of this kind.--Amer. Jour. of Science.