RECENT WORK I\ AGRICULTURAL SCIENCE. 



AGRICULTURAL CHEMISTRY. 



Formation of oceanic salt deposits, .1. II. van't Hon [Zur BUdung der ozeani- 

 dchen Salzablagerungen. Brunswick: Vieweg & Son, 1905, /•/>. 17 85, figs. 34; rev. in 

 Nature [London], ?/ I 1905), No. 1848, pp. 508, 509). — This is the firsl instalmenl of 

 a collection into one publication of the results of the well-known investigations of the 

 author and his collaborators on the formation of double salts, the principal objecl of 

 which was to study the problem of the formation of natural salt beds. 



"The experimental basis of the work is the determination of the solubility, at 

 certain temperatures, of the common salts of the sea, in water and in solutions of 

 each other. With the information so obtained.it is possible to follow exactly the 

 crystallization of a solution containing all these salts, as it gradually loses water by 

 evaporation at the temperature of the experiment. The temperature most used is 

 25° C, which is fairly representative of the temperature of sea water evaporating in 

 Bait gardens, such as those of Hyeres or Cadi/ in summer. 



" When average sea water has been evaporate. 1 down to the point at which chlorid 

 of sodium begins to crystallize, the liquor contains (in molecular proportions LOO 

 Nad. 2.2 KC1. 7.8 MgCl 2 , 3.8 MgS0 4 ; and this mixture of salts is associated with, 

 roughly, 1,000 molecules 11J> (exactly 1,064). On allowing this liquor to evaporate 

 at25°C, the crystallization follows a definite route, which can be traced exactly 

 and without difficulty on one of those marvellous charts representing the march oi 

 physical and chemical phenomena with which the resourceful inventiveness of van't 

 11 off has familiarized us. 



" The crystallization takes place in four acts corresponding to the regions in the 

 chart. 



"(1) Rock salt: Separation of chlorid of sodium in great abundance. Of the LOO 

 NaCl present when crystallization began, only 4.»> NaCl remains dissolved; the 

 remainder. 95.4 NaCl, has been deposited. 



2 Kieserite region: Separation of chlorid of Bodium, sulphate of magnesium, 

 and kaimt (MgS0 4 . KCI. 3H 2 0). The salt separated in this act consists of 4.42 NaCl, 

 2.02 KC1, and 3.07 MgS0 4 ; or, 4.42 NaCl, 1.05 MgS0 4 , and 2.02 kamit. 



( 'arnalhte region: Separation of chlorid of sodium, cai nallite ( KMgt !l s . 61 1 < ' . 

 and kieserite | MgSt >,. II, < )), and the amounts separated are 0.03 Nat '1. i». I carnalhte. 

 and (I.: 1 ..") kieserite. 



"(4) Final liquor: What remains solidifies to 0.15 NaCl. 7.0L' MgCl* (bischofite), 

 ".us carnallite, and ::n kieserite." 



A technical method for the determination of free phosphoric acid in super- 

 phosphates, Gerhardt i Chem. Tig., 29 {1905), No. 14, pp. 178, 179). — The method 

 proposed is a- follows: shake 20 gm. of the superphosphate mixed with 1 gm. ol 

 terrocyanid oi potassium dissolved in a little water for \ hour in 1 liter of water and 

 filter; add a known weight ol calcium carbonate to loo <v. of the filtered solution 



and stir lor \ hour: remove the excess oi calcium carbonate by ans of a quick 



filter, wash a little, dry, burn, ignite carefully, and weigh. The difference between 

 the calcium carbonate used and that thus obtained furnishes a mean- ol calculating 



the free phosphoric acid. 



7:}2S-Nn. i>— or) 2 111 



