•3:l8 



NATURE 



\August 4, 1887 



Chemical Affinity and Solution. 



In continuation of my inquiry into the relation between 

 chemical afiSnity and solution (Nature, vol. xxxiii. p. 615, and 

 and vol. xxxiv. p. 263) I would direct attention to some remark- 

 able facts in connexion with the heats of formation of the sul- 

 phates. Take H2S04Aq, and assume that SO3 acts on the O of 

 water with the average eoergy with which the S acts on O3, and 

 we have the following : — 



[Hg.O] = 68360 [H2S,04Aq] = 210770 



[8,63] = 103240 



[s, FI2] = 4740 

 [S03,0]- 34413 



210753 = 210770 



Now consider BaS04. We have [Ba, 8,04] = 338070 and- 



[Ba,0] = 124240 

 [S.Og] = 103240 

 Difference = 1 10590 



338070 



338070 



The difference 1 10590 is almost exactly equal to [Ba,S] = 

 109600, so that the heat of combination of BaO with SO3 is 

 practically equal to [Ba, S], and the whole of the affinity of S 

 is used up so that it has no power to act on the O of water, and 

 hence the salt is insoluble. 



Take again in the same manner SrS04, and the result is even 

 more striking — 



[Sr,0] = 128440 [Sr,S,04] = 330900 



[8,03] = 103240 

 Difference = 99220 



330900 



330900 



Difference 99220 = [8r,S] = 99200, and again we have an 

 insoluble salt. This seems to me pretty strong evidence that 

 the cause of these combinations is the affinity of 8 for the metal, 

 and that the 8 cannot act on the water to cause solution, because 

 of its intense affinity for the metal. Further, the heat of neu- 

 tralization is the difference between the heat of solution of 

 the oxide and 8O3 on the one hand, and the heat of [M8] on 

 the other, thus : — 



[8rO,Aq] = 29340 



[S03,Aq] = 39153 



Neutralization = 30710 



99203 = [8r,S] = 99200 

 and so on in other cases. 



Now examine CaS04, which is a sparingly soluble salt, and 

 note the difference, we have — 



[Ca,0] = 130930 [Ca,8,04] = 318370 



[8,03! = 103240 

 Difference = 84200 



318370 318370 



This difference, 84200, is not equal to [Ca,8], which is =92000, 

 or 7803 units more, and accordingly we find this salt slightly 

 soluble with a heat of 4440 units, because the 8 is somewhat free 

 to act on water. Further, we have the remarkable fact that 

 CaS04 combines with 2H2O, and evolves in so doing 4740 

 units of heat, which is exactly equal to [8,H2]. Evidently 

 the whole of the affinity of 8 for Ca not being used up in 

 CaO,S03 the 8 can act with its full energy on the H of the 

 water. MgS04, which is a still more soluble salt, shows 

 entirely analogous results, the freedom of the 8 to act on 

 water being much greater than with CaSOa. 



Take now an example of a somewhat different nature ; consider 

 the following : — 



[Na2,0] = 99760 [Na2,8,04,loH20] = 347810 



[8,03] = 103240 

 Difference = 144810 



347810 



347810 



The heat of [Nag, 8] is only 88200 units, but the heat of 

 solution of NagO is 55500, and these two make up very nearly 

 the difference of 144810 units. Thus we have the affinity of the 



S entirely used up, but the affinity of the Nag for the oxygen of 

 the HgO is so great that it can combine as a crystal with ten 

 molecules, in addition to combining with the 8O3. 



If space permitted, these facts might be extended and gone 

 into more minutely, and their complete agreement in every 

 particular with my theory of solution pointed out. 



I may add further that the amount of salt dissolved in saturated 

 solutions which I have examined is in complete harmony with 

 that theory, as the following example will show : — 



Heat of Combination. 

 [M,Cl2] - [M,0,Aq] 

 Ca = 20560 

 Sr = 26770 

 Ba = 35980 



Amount of Salt in Saturated Solution. 

 MCI2] 

 63 grains 

 46 „ 

 35 .. 



It is evident at once that the amount of salt in solution is 

 almost exactly inversely as the difference of heat of [M,Cl2] and 

 [M,0,Aq]. Wm. Durham. 



Early Perseids. 



From my observations in preceding years I found the 

 great shower of Perseids commenced on about July 25, and that 

 the last visible traces of it were seen on August 22, after a 

 duration of 29 days. 



This year a series of very clear nights occurred on July 16, 18, 

 19, 20, 21, 22, 23, 27, 28, and 29, and I watched the sky attentively 

 throughout each one, with the idea of tracing, if possible, the 

 earlier stages of this famous shower. On the i6th there were 

 certainly no Perseids visible, but on the i8th, at iih. im., I 

 saw a brilliant streak-leaving meteor in Andromeda, which must 

 have belonged to this stream. On the 19th I recorded 4 Per- 

 seids (2 of which wei^e brilliant), and the radiant-point was 

 sharply defined at 19° -f 51°. On the 20th and 21st I noticed 

 several other Perseids, but they were too distant from their 

 radiant, and the paths too few to indicate a good centre. On 

 the 22nd, however, I saw 5 Perseids (one of which was as 

 bright as Jupiter), and the radiant now appeared at 25° -f 52°. 

 On the 23rd I registered 4 Perseids, apparently from the same 

 point of the heavens. 



The few ensuing nights were cloudy, but on the 27th the sky 

 became partly clear, and in 3 hours I counted 38 meteors, of 

 which 5 were Perseids from a radiant at 29° -I- 54°. On the 

 28th in 3I hours I saw 47 meteors, though clouds were very 

 prevalent all night. On this occasion 10 Perseids were seen 

 from a centre at 30° ■\- 55°, and there were 15 Aquariads from 

 337° - 12°. On the 29th the sky was almost uninterruptedly clear, 

 and in 3f hours I recorded 52 meteors, including 10 Perseids 

 from 31° -f 54^. On the 30th, clouds prevailed. 



Between July 16 and 29 I observed 287 meteors, of which 43 

 were Perseids. These observations prove that the display really 

 begins a week earlier than that (July 25) given in my paper in the 

 Monthly Notices of the Royal Astronomical Society, vol. xlv. 

 p. 97. The displacement of the apparent radiant-point as there 

 described is well confirmed by my new observations. During the 

 interval from July 18 to August 22 this point advances from 



19° + 51° to 77°+ 57°- 



I subjoin the observed paths of a few bright meteors seen 

 during my recent observations : — 



Path. 



July 19 .. 



h. m. 

 II 43 ... 



11 43 ... 



12 25 .., 

 12 52 ... 

 10 59 ... 

 12 21 ... 



12 25 ... 



13 IS ... 

 13 35 - 



10 40J... 

 13 21 ... 



11 28 ... 



• 358J-I-38 to 3SI -1-30 ... 

 . 298 -f 56 „ 14 -t- 65i ... 

 . 350 +62 ,, 330j-f64 ... 



9 -t- 20 ,, 17 H- 20J ... 

 . 16 -I- 41 .1 i6i-f5i ... 



• 356 +.45 ,. 332 +29 ... 



• 344 + 33 ., 320 -f 29 ... 



• 323 + 37 » 355? + i.oi — 

 . Ill -)- 30 seemed stationary 



325 -[- 6 ,, 330 -I- 8 ... 



319J-I- i6i,, 308 -f 32 ... 



66 -f-72j,, 114 -1-70 ... 



Many others were seen of ist mag. A perfectly stationa 

 meteor of the 2nd mag., and sparkling like a star, was visible 

 July 29 at I4h. 17m. at 337°- 12°, so that it was an Aquaria 

 travelling directly in the line of sight. 



On the 22nd I registered some brilliant meteors, of precise! 

 the same visible type as the Perseids, from a radiant at 16° + 31 

 or 3° south of j8 Andromedae. Many meteors have also bee» 

 faUing from the points 269° + 49°, 310° -f 9°, 333° -f 12", 



