480 Mr. W. Crookes on the Atomic Weight of Thallium. [June 20, 



its way into the bulbs, forms a capillary orifice. By heating the bulb, and 

 immersing the orifice in the pure nitric acid, the acid is introduced into 

 the bulbs h and the globe b until all the thallium has been dissolved. 

 The most tedious part of the process then commences, the evaporation of 

 the excess of free acid. For this purpose an apparatus is used of the form 

 represented in fig. 13 : a is the apparatus, connected by a wide tube (b) 

 and a narrower glass tube with a Woulfe's bottle (c) ; this is in connexion 

 with a Bunsen's water-pump (J), having 15-feet fall of water, and capable 

 of producing an exhaustion equal to 10 inches of mercury. In the course 

 of time the nitrate of thallium is left in the form of dry white crystals. 

 The pump is theu stopped, and air allowed to enter the apparatus by 

 opening the pinch-cock, e, connected with the chloride- of-calcium tuhes, 

 /. The nitrate of thallium is then treated with a solution of oxalic acid 

 to reduce any pernitrate that may be formed, the crystals dried, fused, 

 dissolved in water, again allowed to crystallize, the evaporation of the 

 water being repeated under diminished pressure. When there is no longer 

 a loss of weight, the nitrate of thallium is finally weighed, the air being 

 exhausted from the apparatus. The apparatus is now of the form shown 

 in fig. 14, and is weighed at two different atmospheric pressures. The 

 nitrate of thallium haviug been afterwards removed, the apparatus is alone 

 weighed at two different pressures. There have thus been obtained : — 



a. The weight of the glass + thallium. 



/3. The weight of the glass + nitrate of thallium. 



y. The weight of the glass alone. 

 Particulars of these weights are given in the next section. 



SECTION V. 

 Calculation of the Results. 



The formulse by which I have calculated the weights from weighings at 

 two different atmospheric pressures are given at length in the full descrip- 

 tion of the processes that I have the honour to submit to the Royal 

 Society. 



Collecting the data, we have :— - gfrs. 



True weight of thallium in vacuo =183*790232 



True weight of nitrate of thallium in vacuo = 239*646066 



True weight of glass =766-133831 



(a) Weight of thallium according to true 



value of weights in air =183783921 



(£) Weight of nitrate of thallium in air 



(1005*425937-765*814578). . .. =239*611359 



(c) Weight of glass &c. in air =765*8145/8 



Weights employed to balance («) =183*8099 



Weights employed to balance (b) 



(1005*4364-765*8081) =239*6283 



Weights employed to balance (c) =765*8081 



