SiS Dr. Playfair on the Nitroprussides, 



Then making 



- /A'^F= G, - fCdP'^K, &c., 



we shall have 



V 



y= — =S(G + Hju,i) cosi(p + 2(K + Lvi)sin?(p 



for the effect of the disturbing force of the sea arising from 

 equations of short periods. This is precisely similar to the 

 value of 2/ given above, resulting from the action of the planet. 

 This force, therefore, if sensible, makes no alteration in the 

 general form of y, but only in the value of the numerical co- 

 efficients. This investigation may also include the irregu- 

 larity of the action of gravity arising from high mountains and 

 shores, which may in some places produce as much effect as 

 the disturbing force of the water itself But the effect of these 

 causes is generally insensible ; it is therefore unnecessary to 

 dwell upon it, and the more so as we are not able to compute 

 its exact numerical amount. 



If the additional terms in the value of y which have been 

 found in these two papers be very small in some places, as 

 they no doubt will be, they may yet be considerable in others, 

 and it may be necessary, therefore, to take account of them in 

 order that theory and observation may everywhere accord. 



Guntliwaite Hall, near Barnsley, Yorkshire, 

 March 7, 1850. 



XLIII. On the Nitroprussides, a New Class of Salts. 

 By Dr. Lyon Playfair, F.R.S., F.C.S. 



[Concluded from p. 283.] 



Section IV. — Action of Caustic Alkalies on the Nitroprnssides. 



25. VITHEN a dissolved caustic alkali, such as potash or 

 ^^ soda, is added to a solution of a nitroprusside, the 

 dark red colour of the solution changes to an orange-yellow. If 

 both solutions have been moderately dilute, no oxide of iron is 

 precipitated, nor is ammonia evolved. The addition of alcohol 

 to the orange-yellow liquid causes the precipitation of an aque- 

 ous solution of a new salt. This salt may be procured in a solid 

 state as follows. Nitroprusside of potassium is dissolved in 

 water and double its volume of alcohol is added. Caustic 

 potash is now added to this solution, and a yellow curdy pre- 

 cipitate is obtained. This precipitate is washed with alcohol 

 to free it from an excess of either of the reagents, but it is 

 almost impossible to remove the last traces. The salt is now 



