294 A. W. Witkowski on the 



perfect tightness a circular perforated plate of lead, dd, care- 

 fully cleaned, is placed between the flat end of B and the 

 bottom of the corresponding boring in A. Through the pres- 

 sure of the screw the hole in the lead plate gets reduced to a 

 very small size, and at the same time a perfect pressure-tight 

 connexion is ensured. It is necessary, however, that the 

 metallic surfaces in contact be quite clean and bright. 



To shut up the compressed gas in the bulb two steel screw- 

 valves, K, are employed (one is shown in the figure) . They 

 consist of a cylindrical spindle, carefully turned and polished, 

 provided with a conical end ; near the outer end a screw- 

 thread is cut, working in the screw-head G. By means of 

 the same screw-heads G a number of leather rings, cleaned 

 with ether and impregnated with beeswax and paraffin-oil, 

 are compressed in the stuffing-boxes around the cylindrical 

 polished parts of the spindles. This mode of tightening proved 

 perfectly capable of withstanding the highest pressures em- 

 ployed, although the tightening of the screw- valves is far 

 less important than that of the channel r s t, which is effected 

 solely by contact with metallic surfaces. 



On both sides of the channel r s there are two metallic out- 

 lets, C and D, soldered to A. Through C (fig. 2) the bulb s 1? 

 and similarly s 2 , is charged with compressed gas ; to do this 

 simultaneously in both bulbs, stout copper tubes of small 

 bore, soldered in C and C, are connected by means of a metallic 

 T-tube with the reservoir Z (fig. 1) containing compressed 

 air. In the connecting-piece another screw-valve P is in- 

 serted, through which the interior of the bulbs may be made 

 to communicate with the atmosphere. The valves S^ and N 2 , 

 facing C and 0, will be called here for brevity the " charging 

 valves." 



Through the second pair of outlets D and D (fig. 2) the 

 charges of air, compressed in the bulbs s, are delivered for the 

 purpose of measurement; this is done by unscrewing the 

 u discharging valves" R x and R 2 (fig. 1). 



The measurement of gas-quantity has been effected in 

 special glass flasks E x and E 2 (fig. 1), which may be called 

 eudiometers. For the sake of distinctness of drawing, E 2 and 

 E 2 are represented in the figure on opposite sides of the appa- 

 ratus ; in reality they were placed near one another. 



The discharging-tubes D and D were connected with the 

 eudiometers by means of capillary copper tubes a l9 a 2 (fig. 1) , 

 ending on the eudiometer side in perforated steel stoppers; 

 these were cemented in the upper ends of the eudiometers by- 

 means of sealing-wax. 



Each eudiometer consists of a vertical glass tube, some 



