^ SciaUific Notlcei-^Chemhtry. [J«£*| 



and from the subsidiary Tables Land II. opposite the given day,: 

 the logs, of A, B, C, D, with their prajjer signs ; which' must be 

 written down under the preceding logarithms: then add each 

 pair A, a; B,^; &.c. together; and take out respectively the natu- 

 ral numbers corresponding to the sum of the two logarithms ; 

 and observing that the signs only affect the resulting natural 

 numbers, incorporate them by addition or subtraction accord- 

 ingly ; the amount will be the total correction required ; that 

 atlsmg from rt, b, c, dy being the correction in AR ; that, from* 

 a', A', c', d', the correction in Declination. 



The tables are arranged to mean solar time, which, it is 

 presumed, will extend their utility. And it may be observed, 

 that, by way of artijidal memorj/ to facilitate the recollection of 

 the precise subject to which each column refers (as in B for 

 Bessel, P for Piazza, already mentioned), Mr. Baily has made 

 A B represent the quantity by which the A B erration is deter- 

 mined, C the quantity by which the pie C ession is determined, 

 and D that by which the D eviatioti or Nutation is determined. 

 These contrivances, though avowedly subordinate, will not be 

 despi&ed by those who know how much the pursuits of science 

 are at all times promoted by the introduction of a happy techni- 

 cal mnemonics. / 

 ; After the reading of this elaborate and interesting paper, the 

 Society adjourned to Friday the 11th of November next. 



Article XIII. 

 SCIENTIFIC NOTICES. 



Chemistry. 

 1. Preparation of pure Potash, 



Mr. Donovan proposes the following as a more easy method 

 of obtaining pure potash than the methods commonly employed. 



The crystallized bicarbonate of potash of the shops is to be 

 purified by dissolving it in water at the temperature of 100°. 

 The saturated solution must be! filtered and poured into a flat 

 dish, and placed before the fire; in a few hours a crop of crys- 

 tals of the pure bicarbonate will be obtained. The crystals may 

 then be rinced with a very small quantity of water, and dried on 

 blotting paper. ' i > ; 



The crystals are ndw'tO'be<dissolved in water, and boiled with 

 their own weight of hydrate of lime for 15 minutes ; the solution 

 is then to be ^^fi^'pd j^,j|ti^. usual manner.* We have thus at 



.ii/u.>)>2.i ^.i;J<j!>b 

 * In our n^t-we shall give »' description; of the simple but ingenious apparatus 

 invented by IVnC Donovan for filtering solutions out of contact with the atmosphere.—' 



