210 ANNUAL OF SCIENTIFIC DISCO VEHY. 



MANUFACTURE OF CHLORINE. 



When air is passed through a mixture of ^InO and CaO, sus- 

 pended in water, there is formed manganite of calcium, a compound 

 of MnOo aud CaO. This compound, porpctuaily regenerated, is 

 used in the manufacture of ciilorine as follows : The residual 

 liquor, after a charge of MUO2 has been acted upon by chlorhy- 

 dric acid, is treated with twice the quantity of lime necessary to 

 decompose the chloride of manganese ; and through the resulting 

 precipitate suspended in the liquor air is passed, forming the 

 manganite, which is used agaia to generate chlorine. — W. Whel- 

 dcn before the Brit. Ass., 18C9. 



FILTRATION. 



The operation of filtration being one of constant necessity, and 

 occupying so much time in any analytical operation, attempts 

 have often been made to improve the common method with a 

 view of shortening the time required. Various devices have 

 been proposed to utilize the principle of the syphon; and in 18G5 

 Piccard proposed to filter under pressure by fitting the funnel 

 into a fiask in which the air was rarefied. This rarefaction was 

 eflected by connecting the ilask with a tube through which a thin 

 stream of water flowed, sucking down with it a continuous stream 

 of air-bubbles. No one, has, lnjwever, devised a simple and 

 inexpensive apparatus suitable for general use until reeentl}'. 

 Bunsen ("x\nu. dcr Ch. u. Ph.," vol. xlviii., p. 269) has pub- 

 lished a paper " On the Washing of Precipitates," * of which the 

 following is an abstract : — 



"A precipitate is washed either by filtration or decantation, or 

 b}' a combination of these two methods. In either case the time 

 required is so long, and the quantity of wash-water needed is .--o 

 great, that some simplification of this continually recurring opera- 

 tion is in the highest degree desirable. The following method, 

 which depends, not upon the removal of the impurity by simple 

 attenuation, but upon its displacement by forcing the wash-water 

 through the precipitate, appears to me to combine all the requisite 

 conditions, and therefore to satisfy the need. 



•'The rai)idity with which a liquid filters depends, other things 

 being equal, upon the diff'crenee which exists between the pres- 

 sure on its upper and lower surfaces. Supposing the filter to 

 consist of a solid substance, the pores of wiiich suffer no altera- 

 tion by pressure or by any other influence, then the volume of 

 liquid filtered in a given time is nearly i)rop()rtional to the dif- 

 ference in pressure, as was experimentally shown, using pure 

 water and a filter of artificial pumice-stone. With a difterence 

 of pressure amounting to 0.179 metre the time required for a 

 given quantity of water to run through was 91.7", while under 



• Repriuted in Silliman's Journal, May, 18C9. 



