and its relation to Ozone. 55 



nearly corresponding experiments. A further difficulty also 

 occurred at the commencement of the investigation : it regards 

 the connexion of the various pieces of apparatus. This can 

 neither be effected by cork, india-rubber, or any other organic 

 substance. It is necessary therefore either to fuse together the 

 separate pieces of glass tube forming the apparatus, or where 

 this is not practicable, to unite them by grinding them one into 

 the other. The presence of free hydrogen in the gas containing 

 the ozone must also be avoided, for reasons which I will give 

 hereafter. Lastly, even the proportions of the apparatus are 

 confined within certain limits ; the slowly moving stream of gas 

 requires a space of time sufficient for the spontaneous decompo- 

 sition of a considerable quantity of ozone before arriving in the 

 solution of iodide of potassium. 



Plate I. fig. 1 shows the apparatus employed in the experi- 

 ments. It is divisible into three parts ; the first (fig. 2) serves 

 for the evolution of the oxygen containing the ozone, the second 

 (fig. 3) serves to dry the gas, and the third (fig. lA) is for the 

 reception of the products of the decomposition of the ozone. 



A wide tube (fig. 2a), which is intended for the reception of 

 the porous cell b, has smelted to it another tube, such as is used 

 for the ordinary evolution of gas. About an inch above its lower 

 end a platinum wire, to which a platinum plate is attached, is 

 fused in. The latter serves as the positive pole, and reaches 

 down into the porous cell, which is open at both ends. A second 

 tube (fig. 3), which may be conveniently slipped over the pre- 

 ceding, is united by a thinner tube e to the drying apparatus 

 / (comp. fig. 1). In this case also the separate pieces of tube 

 are fused together. This second tube (fig. 3) rests with its lower 

 end upon the funnel-shaped enlargement a of the first tube, fig. 2; 

 its upper end projects about an inch beyond the top of the first 

 tube. The drying-tube represented at / (fig. 3) has the inclina- 

 tion shown in fig. 1 ; it is 3 feet long, and has the diameter of a 

 wide combustion-tube. It contains pumice-stone saturated with 

 chemically pure concentrated sulphuric acid. To get rid of any 

 sulphurous acid, the smallest quantity of which would frustrate 

 the whole experiment, the pumice-stone is previously moistened 

 with pure sulphuric acid, and repeatedly heated to redness 

 throughout. It fills the tube up to the anterior end, whilst the 

 sulphuric acid collects in the hinder portion, which is bent down, 

 and even runs back in part into the narrow connecting tube. In 

 this manner, the gas, after passing the stratum of sulphuric acid, 

 forms bubbles, which pass gradually through the fragments of 

 pumice-stone. Over the anterior end of the drying tube a closely 

 fitting cap (fig. 4) is now passed. This consists of a wide test- 

 tube, to which a short piece of narrower tube has been attached 



