CARRIERS, MECHANICAL. 



CHEMISTRY. 



99 



but provided with an elastic attachment which 

 fills the tube and prevents the passage of air. 

 In the exhaust or vacuum systems the air is 

 drawn from the tube in front of the carrier, 

 and the motive force is derived from the natu- 

 ral atmospheric pressure of about fifteen pounds 

 to the square inch. The air current has to be 

 kept up constantly in order to afford a uniform 

 and trustworthy service, and the circulation of 

 air is an important consideration in a crowded 

 establishment. 



In the systems operated by compressed air 

 the current is in motion only when actually 

 required. In stores of moderate size, foot- 

 power air-pumps are used, with highly satis- 

 factory results. The fixtures at either end of 

 such a line are shown in Figures 12 and 13, 

 the tubes being carried under the counters or 

 floors, or overhead if more convenient. A 

 salesman (Ffg. 13) is represented in the act of 

 sending a carrier. After dropping the carrier 

 into the receptacle he turns the small handle 

 at the side, clo*sing a valve within the tube, and 

 then steps upon the air-pump lever. A slight 

 pressure only is necessary to deliver the carrier 

 in an instant at a distance of 150 feet. Releas- 

 ing the handle, the valve opens automatically, 

 and the tube is ready for the return carrier. If 

 the valve at either end is closed, the operator 

 at the other end is instantly aware, from the 



large establishments a central air-compressor 

 is worked by machinery, and no foot-power is 

 required, the compressed air being furnished 

 from a central receiver, and turned on by sales- 

 men or cashier as required at each station. 

 Cash and parcel carriers are generally rented 



CASHIER, PNEUMATIC SYSTEM. 



resistance of the air-pump, that the tube is not 

 clear. At the delivery end the carrier is shot 

 out, falling upon a cushion, as shown in the 

 engraving of the cashier's desk (Fig. 12). In 



SALESMAN, PNEUMATIC SYSTEM. 



out to merchants at so much a station, the 

 price ranging from $15 to $30 per annum. 

 Each station is supposed to be equivalent or 

 superior in efficiency to the average cash-boy, 

 without any of his mischievous propensities. 

 The saving, therefore, in wages and responsi- 

 bility is very considerable where a good store- 

 service system is introduced. 



CHEMISTRY. Chemical Philosophy. -The de- 

 termination and graphic representation of the 

 constitution of matter, is the subject of one of 

 the most notable of recent papers in this de- 

 partment of chemical science. The article 

 appeared in "Nature," and begins with the 

 declaration that the growth of the science of 

 organic chemistry is to be measured, not so 

 much by the innumerable new compounds 

 which it has brought to light, as by the unfold- 

 ing of its doctrine of constitutional formulas, 

 this being the particular contribution which it 

 has been able to make toward solving the cen- 

 tral problem of all chemistry the constitution 

 of matter. That as a whole these formula 



