The Rh(I) iodocarbonyl complexes [Rh(CO)(L Me ) 2 I] (3a) and [Rh(CO)(L Mes ) 2 I] (3f) (L Me ) 3,5-dimethylimidazoline-2-ylidene; L Mes ) 3,5-dimesitylimidazoline-2-ylidene) have been prepared by the reaction of [Rh(CO) 2 (OAc)] 2 or [Rh(CO) 2 (acac)] with an imidazolium salt in the presence of Cs 2 CO 3 . Complex 3a reacts with MeI to give a Rh(III) acetyl complex, [Rh-(L Me ) 2 I 2 (COMe)] (5a), which is unstable and decomposes by elimination of MeI to regenerate 3a. Rate and equilibrium constants have been measured for the reversible reaction 3a + MeI f 5a. Thermodynamic parameters indicate that the forward reaction is exothermic (∆H ) -51 ( 3 kJ mol -1 ) but disfavored entropically (∆S ) -159 ( 12 J mol -1 K -1 ). Complex 3f does not react with MeI. The results are compared with data reported for [Rh(CO)(PEt 3 ) 2 I], and the differences in behavior of the N-heterocyclic carbene and PEt 3 systems are interpreted on the basis of ligand steric effects. An X-ray crystal structure is presented for [Rh(L Me ) 2 I 2 -(OAc)] (6a), and a mechanism is proposed for its formation from 5a. Tests on 3a as a catalyst for the carbonylation of methanol indicate sequential loss of the two L Me ligands and formation of [Rh(CO) 2 I 2 ] -.
It is now a year and a half since I communicated to this Society a description of a portable form of apparatus for enabling us to count the number of particles of dust in the atmosphere. The working of that instrument in my hands has been most satisfactory, and though it has occasionally given trouble, yet it has not given more than might have been expected. Though that apparatus has worked quite pleasantly with me, and enabled a beginning to be made of an investigation into the amount, and the effects, of dust in our atmosphere, yet very few have as yet followed up this line of inquiry. This has probably been owing to there being something in the complicated nature of the apparatus which has deterred others from joining in the work. I therefore determined to see if a simpler, and at the same time a reliable, form of the apparatus could not be devised.
In a previous communication I described the apparatus first used for counting the dust particles in the atmosphere. That apparatus was constructed of such materials as could be easily obtained ready made, and was fitted together in such a way that any one acquainted with laboratory work could easily repeat the experiments. Though that apparatus is satisfactory enough for preliminary work, and gives fairly good results, yet it is evidently not suited for regular everyday use; and, besides that, there are certain defects in it which can be avoided in apparatus specially constructed.
The portable dust-counting apparatus described in a previous communication to this Society was designed with a view of making observations on the air at situations where it would be inconvenient to work with the larger laboratory apparatus; and also to enable these observations to be made under conditions more favourable for avoiding local impurities than is possible when working in a house. As the construction of this portable apparatus was completed just as I was about to start for the Continent, the opportunity seemed a favourable one for continuing the investigation into the number of dust particles in the atmosphere, and extending our knowledge on the subject in other countries. The portable apparatus is reduced to such dimensions that it adds but little to one's personal luggage, and can be easily carried to’ the place where the observations are to be made.
Water is perhaps the most abundant and most universally distributed form of matter on the earth. It has to perform more varied functions and more important duties than any other kind of matter with which we are acquainted. From its close connection with all forms of life, it has been the subject of deepest interest in all ages. It is constantly changing from one of its states to another. At one time it is solid, now liquid, and then gaseous. These changes take place in regular succession, with every return of day and night, and every successive season; and these changes are constantly repeating themselves with every returning cycle. Of these changes, the one which perhaps has the greatest interest for us, and which has for long ages been the subject of special observation, is the change of water from its vaporous state, to its condensation into clouds, and descent as rain. Ever since man first “observed the winds “and “regarded the clouds,” and discovered that “fair weather cometh out of the north,” this has been the subject of intensest human interest, and at present forms one of the most important parts of the science of meteorology, a science in which perhaps more observations have been made and recorded than in all the other sciences together.
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