18 Col. Yorke on the Solubility of the Oxide of Lead. 



a paper filter. It is to this opinion that I propose to direct 

 attention in the present notice. 



The fact that the aqueous solution of oxide of lead would 

 not pass through a filter was noticed by me in the paper al- 

 ready referred to ; but as the action of tests on the liquid was 

 just what one observes with solutions; as no time allowed for 

 subsidence made any difference in these appearances ; as the 

 liquid deposited crystals of oxide of lead not only on the lead 

 but on other bodies ; as when decomposed by the voltaic bat- 

 tery it gave metallic lead at the negative pole, and peroxide 

 at the positive; I did not consider that the stoppage of the 

 oxide of lead by the filter was any proof of its not being dis- 

 solved. There still, however, remains this question to be an- 

 swered, — In what way does the paper act in retaining the ox- 

 ide? and I think that the following experiments afford an 

 answer to the question. 



I placed some clean rods of lead in bottles of distilled water 

 loosely stoppered ; in this way, after removing the rods of lead, 

 I obtained a clear liquid, which, when tested by sulphuretted 

 hydrogen, gave a deep brown colour. On passing this liquid 

 through a double filter, which had been previously washed 

 with hot distilled water, it appeared to be very nearly deprived 

 of lead: when two or three fluid ounces had passed through, 

 the filters were removed, washed, then immersed in a solution 

 of sulphuretted hydrogen, again washed and dried. Some 

 torn fragments of the filters were then mounted in Canada 

 balsam for examination by the microscope. On examination 

 with powers of from 1 50 to 400, the fibres of the flax com- 

 posing the paper were seen to be browned, and in many in- 

 stances it could be distinctly observed that the colouring sub- 

 stance occupied the interior of the tubular fibre. Now, it is 

 stated by Mr. Crum, in the Philosophical Magazine for 

 April 1844, that cotton wool possesses the power of abstracting 

 the oxide of lead from its solution in lime-water, and that this 

 property is made available in the processes for dyeing cotton 

 with the chromates. I found that on filtering a solution of 

 oxide of lead in lime water through a triple filter, that whereas 

 the original solution gave a deep black when tested by sul- 

 phuretted hydrogen, the filtered liquid gave but a pale brown ; 

 and it required that the unfiltered liquid should be diluted 

 with thirty times its volume of water to produce the same test 

 as the filtered. 



I then tried the effect of mere immersion of the paper in the 

 aqueous solutions before used. A bit of filtering-paper ten 

 inches by two inches was boiled in distilled water and then 

 put into an ounce phial filled with the aqueous solution ; after 



