212 



ferment which is capable of elfecting in any considerable degree the 

 decomposition of rubian, as the best proof of its being a pecu- 

 liar and distinct substance. When prepared by precipitation with 

 alcohol, erythrozym is obtained as a chocolate-coloured granular 

 mass. When dried it coheres into hard lumps, which are almost 

 black, and with difficulty reduced to powder. When the dry sub- 

 stance is heated on platinum foil, it emits a smell somewhere between 

 that of burning peat and burning horn, and then burns without much 

 flame, leaving a considerable quantity of residue, which on being 

 further heated is soon converted into a white or grey ash. 



After having once been precipitated from its watery solution, even 

 by alcohol, erythrozym cannot again be dissolved in water. If it be 

 mixed while in a moist state with water, it forms a reddish-brown 

 turbid liquid, in which it exists however merely in a state of suspen- 

 sion. Erythrozym is not an uncombined substance, but is a definite 

 compound of an organic body with lime. When treated with acids 

 the lime is removed, and the colour of the substance changes from 

 reddish-brown to yellowish-brown. If a mixture of erythrozym and 

 water be allowed to stand for some time, the former enters into a 

 state of putrefaction, accompanied by a disengagement of gas. After 

 it has entered on this stage of decomposition, it loses in great part 

 the power of decomposing rubian, but acquires that of producing an 

 acid reaction in a solution of sugar. Erythrozym contains nitrogen, 

 but in much smaller proportion than most other fermentative sub- 

 stances. Its composition, when in a freshly precipitated state, is 

 expressed by the formula Cj,^ H34 04o + 4CaO. When allowed to 

 decompose, it loses carbonic acid, water, and lime. A quantity 

 which had been employed for the purpose of effecting the decompo- 

 sition of rubian, and then separated again from the products of the 

 action, had a composition corresponding to the formula C^^Hgo N2O30 

 + 3CciO. 



In conclusion, the author gives the results of some experiments 

 undertaken with the view of ascertaining whether madder contains 

 more than one colouring matter or not. He infers from his experi- 

 ments, that the purpurine of other chemists is not a substance of de- 

 terminate composition ; that it consists sometimes of alizarine alon^j^ 

 sometimes of verantine alone, sometimes of a variable mixture of 

 both ; that only one colouring matter, viz. alizarine, can be obtained 

 from madder ; that purpurine, madder-purple, and the various similar 

 bodies derived from madder, owe their property as colouring matters 

 to an admixture of alizarine; and that they are simply the latter 

 substance in a state of impurity. 



3. " Experiments towards the construction of new forms of Instru- 

 ments for the correction of Compass Errors due to the presence of 

 iron in ships j with investigations on the nature of the attraction of 

 Iron on the poles of Magnets." By Julius Roberts, Esq., Lieut. 

 K.M. Artillery. Communicated by Capt. W. H. Smyth, R.N., 

 For. Sec. R.S. Received March 25, 1852. 



The object of the author's experiments and investigations is stated 



