I SI 4. 3 ^« Iodine. 10^ 



iodine is as 1 to 20, or 15 to 300. With oxymuriatic acid it forms 

 an orange yellow substance, crystalline, volatile, deliquescent, and 

 appearing to exist with two different proportions of iodine. 



Iodine forms, as is known, a fulminating powder with ammonia; 

 but the theory is very simple if we consider that lodme has a great 

 tendency to combine with hydrogen. ' • ^i 



From the preceding statement we cannot but perceive the 

 analogy between iodine and chlorine, the new acid and muriatic 

 acid It is very remarkable that hydrogen is always necessary 

 to convert iodine into an acid. This substance appears to act the 

 same part with respect to a certain class of bodies as oxygen does 

 to another. All the phenomena, of which we have spoken, may be 

 explained by supposing iodine to be an element, and to form an 

 acid by combining with hydrogen; or by supposing that j his last 

 acid is a compound of water and an unknown base, and iodine 

 this base united to oxygen. The first hypothesis appears to us, from 

 the preceding facts, more probable than the last; and it serves, 

 at the same time, to give more probability to that which con- 

 siders oxymuriatic acid as a simple body. If we adopt it, the 

 name which seems most suitable to the new acid is hydriodic acid. 



Article V. 



Answer to Dr. Grierson's Observations on Transition Rocks. 

 By Thomas Allan, Esq. F.R.S.E. 



(To Dr. Thomson.) 

 SIR, 

 When men of science have devoted themselves to any particular 

 study, whether for profit or amusement, it is very natural that they 

 should feel a desire of rendering their labours useful to society ; 

 and it sometimes may liappen that such a motive is the only induce- 

 ment that tempts an individual to depart from the privacy ot his 

 study, and submit himself to the indiscriminating censure ot the 

 public; yet how often do we see the critic unjustly garblmg and 

 Interpolating the work of an unfortunate author, and trequently 

 mis-stating facts, merely to give weight to his own argument; hoping 

 that few of those to whom his acrimony is addressed will take the 

 trouble to investigate whether he be in the right or not : and at any 

 rate, that his words, as being the last, will make some impression 

 on a great proportion of those wlio may chance to peruse them. 



From what 1 understand to be the character of the geiillcnian 

 who has taken so mucii trouble in your Number tor August to 

 expose the futility of my ol)iiervations on the transition rocks ot 

 Werner, I am persiuaded he did not allow himself lo wander so 

 much out of the track in which I am told his friends have been in 

 ihc habit of finding,' him, merely for the purpose ol ludulging in 



