OF ARTS AND SCIENCES : JANUARY 29, 1873. 503 



of the Academy. The final result, corrected for Personal 

 Equation, is : — 



Difference of longitude between Cambridge and Dnxbury . . l m 50 s .205 ± .022 

 Difference of longitude between Duxbury and Brest . . 4 h 24 m 43 s .277 ± .047 

 Difference of longitude between Cambridge and Brest . . 4 h 26 m 33 s .482 ± .052 



Professor J. P. Cooke described a method he is employing 

 for the manipulation of hydric sulphide. 



The manipulation of hydric. sulphide in a large laboratory has al- 

 ways been a difficult problem, and the inconveniences arising from the 

 use of this reagent, in the state of gas, are so great, that, when a 

 class of forty or fifty students are working with it at once, the nuisance 

 becomes almost unbearable. When dissolved in water, however, this 

 reagent gives as little trouble or annoyance as any other ; but, as ordi- 

 narily prepared, the solution is so weak that the substance under exam- 

 ination is deluged with water before the required excess of the reagent 

 has been added. This objection can be wholly overcome by dissolving 

 the gas under pressure, and drawing off the solution from a siphon 

 like soda-water, and, in any laboratory where water is supplied under 

 pressure, such a supersaturated solution can be very readily prepared 

 with a very simple apparatus, which may be mounted in the following 

 manner. 



We use for the purpose the common green glass bottles in which 

 acids are usually sold by the druggists, only taking care to select strong 

 bottles with a well-rounded neck about one and a quarter inches in 

 diameter. Let us designate by A, B, and C three two-quart bottles 

 of this description, and by D a similar but larger bottle, having a 

 capacity of two gallons. In A, the gas is generated from ferrous sul- 

 phide, water, and sulphuric acid, in the ordinary way. We pass the 

 gas from A, first through a wash bottle filled with moistened sponge, 

 and through the distilled water with which the bottles B and C are 

 about three fourths filled, the gas bubbling up as usual from glass tubes 

 leading to the bottom of each bottle, and the excess, not absorbed by 

 the water, passing forward to the large bottle C, which serves as a 

 gasometer. All these bottles are fitted as tightly as possible with rub- 

 ber stoppers, through which pass the stout glass tubes that conduct the 

 gas. Through the stopper of D pass three such tubes : the first which 

 brings the unabsorbed gas from C opens at the top of the bottle ; the 

 second is connected by. a rubber hose with a water faucet, and reaches 



