146 Intelligence and Miscellaneous Articles. 



stances, by instrumental comparisons. The index errors are very- 

 constant, and were accurately determined last evening. 



Greenwich M.T. Comet's R.A. Comet's Dec. Weight, 



h m s o I II o I II 



March 30 1 23 40 7 32 27 -1-1 48 43 1 



1 55 8 7 33 56 +1 45 21 2 



In the observations for the first position the centre of the field was 

 estimated, and nine single results are tolerably accordant. The 

 second place depends on one good observation with cross wires, 

 clouds preventing any further comparisons. 



Had the sky been free from the whiteness which is so fatal to 

 vision by daylight, I should have obtained much better places. 



I communicated an ephemeris to Mr. Dawes, who has observed 

 the comet with extreme care, but I do not know at present whether 

 he saw it yesterday in daylight. 



XXVIII. Intelligence and Miscellaneous Articles. 



ON A NEVr TEST FOU PRUSSIC ACID, AND ON A SIMPLE METHOD 

 OF PREPARING THE SULPHOCYANIDE OF AMMONIUM. BY 

 PROF. LIEBIG. 



WHEN some sulphuret of ammonium and caustic ammonia are 

 added to a concentrated aqueous solution of prussic acid, and 

 the mixture heated with the addition of pure flowers of sulphur, the 

 prussic acid is converted in a iew minutes into sulphocyanide of am- 

 monium. This metamorphosis depends on the circumstance, that 

 the higher sulphurets of ammonium are instantly deprived by the 

 cyanide of ammonium of the excess of sulphur they contain above 

 the monosulphuret ; for instance, if a mixture of prussic acid and 

 ammonia be added to the pentasulphuret of ammonium, the solution 

 of which is of a deep yellow colour, and the whole gently heated, 

 the sulphuret of ammonium is soon decolorized ; and when the clear 

 colourless liquid is evaporated, and the admixture of sulphuret of 

 ammonium expelled, a white saline mass is obtained, which dissolves 

 entirely in alcohol. The solution yields, on cooling or evaporation, 

 colourless crystals of pure sulphocyanide of ammonium. Only a 

 small quantity of sulphuret of ammonium is requisite to convert, in 

 the presence of an excess of sulphur, unlimited quantities of cyanide 

 of ammonium into sulphocyanide ; because the sulphuret of ammo- 

 nium, when reduced to the state of monosulphuret, constantly reac- 

 quires its power of dissolving sulphur and transferring it to the 

 cyanide of ammonium. The following proportions will be found to 

 be advantageous: — 2 oz. of solution of caustic ammonia of 0'9^ 

 spec. grav. are saturated with sulphuretted hydrogen gas ; the 

 hydrosulphate of ammonia thus obtained is mixed with 6 oz. 

 of the same solution of ammonia, and to this mixture 2 oz. of 

 flowers of sulphur are added ; and then the product resulting from 

 the distillation of 6 oz. prussiate of potash, 3 oz. of the hydrate of 

 sulphuric acid, and 18 oz. water. This mixture is digested in the 



