474 Intelligence and Miscellaneous Articles. 



comparative value of the African guano as a manure. This depends, 

 first, on the amount of phosphates, and secondly, on that of the am- 

 monia, or substances capable of affording that ingredient. But it is 

 also evident that the state in which the nitrogenous compounds are 

 contained in the manure must be of some importance, i. e. whether 

 they exist in the form of ammonia, as is the case with the guano 

 submitted by us to analysis, or in the state of uric acid % 



It is probable that this African guano would prove extremely 

 stimulating to vegetation at first, but that its power would soon be 

 spent, unless previous to its employment it were mixed with some 

 substance capable of fixing the ammonia, such as gypsum or char- 

 coal, as recommended by Boussingault and Payen ; while that con- 

 taining uric acid would, from the slow decomposition of this sub- 

 stance, prove for a long time a constant source of nitrogen propor- 

 tionate to the growth of the plants. — CJiem. Gazette, May 1, 1844. 



PROCESS FOR OBTAINING IRIDIUM. BY M. E. FREMY. 



In order to obtain iridium, M. Fremy treats the chloride of iri- 

 dium with hydrochlorate of ammonia ; a precipitate of a brownish- 

 red colour is formed, which is a compound of the bichlorides of iri- 

 dium and osmium with hydrochlorate of ammonia ; in order to sepa- 

 rate these a current of sulphurous acid is passed into the two salts 

 suspended in water, by this the iridium is dissolved, and the osmium 

 remains precipitated in the state of a red salt. The soluble salt of 

 iridium thus obtained crystallizes in large brown prisms from solu- 

 tion in hydrochlorate of ammonia ; when it is calcined in a current 

 of hydrogen, it yields pure iridium, which retains the crystalline form 

 of the salt. 



The soluble salt of iridium, under the influence of chlorine, repro- 

 duces the black insoluble salt, and serves for the preparation of all the 

 compounds of iridium. — Journ. de Ph. et de Ch., Mars 1844. 



AN EXPERIMENT FOR RENDERING APPARENT THE ADJUSTING 

 POWER OF THE EYE. BY REUBEN PHILLIPS. 

 If the head be turned away from a window, and if a small bright 

 piece of metal, as a knitting-needle, be held within a few inches of 

 the eye, so that the needle may be distinctly seen, taking care so to 

 place the head as to intercept as little as possible of the light which 

 can fall on the needle ; — things being thus arranged, if the eye be 

 directed to a wall, a few feet distant, for a few seconds, and then, 



* " The value of a manure depends therefore on the proportion of nitrogenized 

 organic matter, and especially in relation to the non-nitrogenous organic sub- 

 stances, and lastly, on the decomposition of the quaternary substances being gra- 

 dually effected, and so keeping pace with the progress of vegetation." And again, 

 " A manure entirely decomposable into its soluble and gaseous products in the 

 course of a single year will be capable of producing as great an effect on the first 

 crop as five times the quantity of another manure which would require five years 

 for its ultimate decomposition, but then the latter will furnish useful products 

 during a period five times longer." — Payen and Boussingault in Ann. de Chim. 

 et de Phys., t. iii. pp. 67 and 70. 



