by firs! in;il<iii,i>' ;i saliirafcd soliilioii al 15". Pure, Mkhck's copner 

 snlpluUe {i'lXHi IVoui iron) was dissolved in water and lM»iled with 

 eo|)|)er liydmxide to remove traces of free acid. Aflei' tiltralioii the 

 li()uid was <'ooI(hI and after inlrodneinii' a crystal of ('uSO,. 5 ll.() 

 set aside to crvstallise. The salt was then siiaken for a lon,<>,- tin)(> 

 (3 to 5 lionrs) with water at 15° in a thermostat, nse heiiii;- nuulc 

 of NoYKs ') shakinu' apparatus. All the thermometers nsed in this 

 investi,iialion \\ere tested by means of a standard tlicrmumclcr IVnin 

 the "Pliysikaliscli-lochnisclie iieichsaiistalt" jit Cluirlotteid)nrLi-. 



To make snre tluit complete satnvation had indeeil been attained 

 we took aftei' 3 and 5 honrs small samples from the solution in 

 the shaking- bottles and analysed these ii(piid bv means of Nki.mann's 

 electrolytic process ^). 



Ill this way we found: 



(5 hours) 100 parts of watei- dissolve 19.22 parts of anhydrous 

 CuSO,. 



(3 hours) 100 juii'ls of water dissoh'e 19.28 parts of anhydrous 

 CuSO,. 



The zinc suljihafe solutions were pi'ej)ai'ed from a solution which 

 was satui'ated at 15° in the same thei'inostat as the coppin- sulphate 

 solutions. The dilferent dilutions were done by wei^hini;-. 



The zinc sulphate ^axe no I'eaclion with couuoi'ed; moreoNcr the 

 same iu'e[)ai'ation had served in the construction of ('i-VKK-cells which 

 appeared to be peilectly correct. By way of a check we also 

 determined the (piantity of ZnSO, which at 15° is present in the 

 saturated solution. A \vei,i>ii(Ml (piantity of the solution was e\aporaIe<l 

 in a platinum dish and the i-esidne (Zn S( )^ . 1 ll.,0) was w(M,<>lie(r'). 

 Ill 100 grams of water we found 50.94 grams of ZnSO^ (as aidiy- 

 dride) whereas previous detei-minations had uiven 50.8(S. If we 

 accept the tiunre 50.94, the satni-ated solution then contains at 15°, 

 150.5(5 o-rams of Zn SO^ . 7 !!.,() to 100 grams of water. We fail to 

 see how Cji.udiku has arrived at the ligure 200 (see table 1). 



6. Measurements with Damki.i.-ccIIs are rather diflicult. for ifllic 

 smallest amount of copper sulphate solution comes in conlaci with 



1) Zeitschr. fur pliys. Cliomio 9, »1(>3 (].s«)i>). 



2) Neumann, Analylischo Elekliolyse der Metallo, (Halle 1S07). Pair. IOC. 



We may casually remark that llie figures triven in the literature lor the solnhi- 

 lity of (•o|)|)er sulphate are ineorreel. Compare: Khnst Cohkn, Vorlra-re fur Aerzte 

 liber pliysikalisclie Chemie (Leip/.iü; lüOl) pag. 70. 



3) See C.\LLKND.\H en Haiunes, Proc. Koyal Society G:i, li7(ib'J7j; Eiin<t Cohen, 

 Zeitschrifl fur phys. Chemie 34, 181 (1900). 



