496 PRINCIPLES OF CHEMISTRY 



an orange colour, and when cooled to 2 yields crystals containing 

 10 molecules of water to 1 molecule of bromine. 60 Alcohol dissolves a 

 greater quantity of bromine, and ether a still greater amount. But 

 after .a certain time products of the action of the bromine on these 

 organic substances are formed in the solutions. Aqueous solutions of 

 the bromides also absorb a large amount of bromine. 



With respect to iodine, it is almost exclusively extracted from the 

 mother liquors after the crystallisation of natural sodium nitrate (Chili 

 saltpetre) and from the ashes of the sea -weed cast upon the shores of 

 France, Great Britain, and Spain, sometimes in considerable quantities, 

 by the high tides. The majority of these sea-weeds are of the genera 

 Fucus, Laminaria, &c. The fused ashes of these sea- weeds are called 

 'kelp' in Scotland and 'varech' in Normandy. A somewhat con- 

 siderable quantity of iodine is contained in these sea- weeds. After 



periment (Van der Plaats confirmed it), bat also by means of the determination of the 

 vapour tensions. For solid bromine the vapour tension p in mm. at t was found to be 



p= 20 25 80 85 40 45mm. 



t= -16'6 -14 -12 -10 - 8-5 - 7 

 For liquid bromine 



p= 50 100- 200 400 600 760mm. 



<=_5-0 + 8-2 28-4 40-4' 51'9 58'7 



These curves intersect at -7 0- 05. Besides which, in comparing the vapour tension ol 

 many liquids (for example, those given in Chapter II., Note 27), Bamsay and Young 

 observed that the ratio of the absolute temperatures (t + 273) corresponding with equal 

 tension varies for every pair of substances in rectilinear proportion in dependence upon t, 

 end, therefore, for the above' pressure p, Bamsay and Young determined the ratio of 

 t + 278 for water and bromine, and found that the straight lines expressing these ratios 

 for liquid and solid bromine intersect also at 7'06 ; thus, for example, for solid bromine 



p=> 20 25 80 85 40 45 



278 + *= 256-4 259 261 268 264'6 266 



278 + *'= 295-8 299 802*1 804*8 807'2 809'8 



c= 1-152 1;154 1-157 1159 1'161 T1B8 



where t' indicates the temperature of water corresponding with a vapour tension .p, and 

 where c is the ratio of 278 + 1' to 278 + 1. The magnitude of c is evidently expressed with 

 great accuracy by the straight line c = 1-1708 + O'OOll*. In exactly the same way we find 

 the ratio for liquid bromine and water to be c t = 1*1585 -f 0-00057*. The intersection of 

 these straight lines in fact corresponds with 7'06, which again confirms the melting 

 point given above for bromine. In this manner it is possible with the existing store of 

 data to accurately establish and verify the melting point of substances. Bamsay and 

 Young established the thermal constants of iodine by exactly the same method. 



60 The observations made by Paterno and Nasini (by Baoult's method, Chapter I. 

 Note 49) on the temperature of the formation of ice{ 1-115, with 1-891 gram of bromine 

 in 100 grams of water) in an aqueous solution of bromine, showed that bromine is contained 

 in solutions as the molecule Br 2 , Similar experiments conducted on iodine (Kloboukoff 

 1889 and Beckmann 1890) show that in solution the molecule is I 8 . 



B. Boozeboom investigated the hydrate of bromine as completely as the hydrate ol 

 chlorine (Notes 9, 10), the temperature of the complete decomposition of the hydrate U 

 + 6-2; the density of Br 8 10H 3 iO = l-49. 



