39 



Apparat i omkring 2 Timer, idet den undvigende Kulsyre 

 som før opfangedes og bestemtes ved 'titreret Barytvand. 

 I den anvendte Mærigde Sodaopløsning var indeholdt H3.3 

 Mgr. Soda svarende til 26:3 Mgr. Kulsyre, medens der 

 ved to Experimenter paa denne Maade fandtes uddrevet 

 den ene Gang 26.8 og den anden -7.7 Mgf. Ved For- 

 sogets Gjentagelse med en lidt større Qvantitet paany ind- 

 v.eiet Soda fandtes uddrevet 34.1 Mur. Kulsyre' istedétfor 

 beregnet 33.2. Under Kogrringen var Opløsriingen i Be- 

 gyndelsen fuldstændig klar. hvorpaa der etter circa l / 2 Ti- 

 mes Forløb begyndte at fremkomme et Bundfald af Mag- 

 nesia, hvori der trods al anvendt Møie ikke rykkedes mig 

 at [Kiavise det mindste Spor at' Kulsyre. . Den basisk kul- 

 sure Magnesia er nemlig ifølge. H. Rose og Flere ikke 

 ubetydelig opløseJig saavel i Vånd som i forskjellige Salte. 

 saaledes at der af smaa Mængder intet Bundfald fremkom- 

 mer, og det er derfor ikke paafaldende, at ( >xydet ved saa 

 forhudede < (pløsninger, som her ere anvendte, ikke udfældes, 

 førend det ved Koeningen er befriet for sin Kulsyre. 



Koges Søvand under Concéntration, kan man meget. 

 let komme til at overse denne Udskillelse af Magnesia, 

 idet denne forst indtræder etter nogeh Tids Forlob. saa- 

 ledes at man kan antage Blakningen fremkommén ved Od- 

 fældning af.Gips i den concentrerede Yædske. Udskillelsen 

 vil ogsaa, naar Inddampningen foregaar i aabént Kar. for- 

 sinkes betydelig!, idet Kulsyrens Undvigen foregaar meget 

 langsommere i en kulsyreholdig Atmosphære end i en kul- 

 syreffi Luftstrøm, og det kan derfor ikke forundre, at 

 denne D/dfældning af Magnesia af kogende' Søvand, saavidt 

 mig bekjendt; ikke tidligere er observeret. naar undtages. at 

 Isiglio 1 i det tørrede Residum har paavist fri Magnesia. 

 Dersom man imidlertid koger Sovand ilden Concéntration 

 i en kulsyrefri Atmosphære med omvendt Kjoler, saaledes 

 som det let kan ske ved Glassens Apparat, fremtræder 

 Phænomenet meget tydeligt paå samme Maade som ved 

 Kogning af en Blanding af Soda og Bittersalt. idet der 

 elter circa 1 j 2 Times Kogning begynder' at udskille - sig et 

 Bundfald bestaaende af ren kulsyre- og kalkfri Magnesia 

 ved Siden af et lidet Spor af Kiselsyre Mdrørende fra det 

 benyttede Glåskar. Om man samtidig opfanger og bestem- 

 mer den undvigende Kulsyre. viser det sig. at den Yillig- 

 hed, hvormed Kulsyren undviger, ikke saameget afhænger 

 af Concentrationsgradén som af Yarigheden af det Tids- 

 rum, hvori Kogningen fortsættes, da ogsaa paa denne Maade 

 circa 2 Timers Kogning strækker til for at skaffe en fuld- 

 stændig kulsvrefri Yædske. 



Det vil forliaalientlig hermed kunne ansees fuldstænr 

 dig godtgjort, at Sovandets Evne til ved Kogning at decom- 



. påratus for. 2 hours exposéd to a current of air frée from 

 carbonic acid. the carbonic acid driven off-being collected 



and deterniined as liefore liv titrated haryta water. The 

 portion of tin- solution of carbonate of soda employed 



contained 63.3 " of that substance, representing 26.3T 



carbonic acid; and t.wo experiments performed by this 

 method gave respéctively 26.8 m " r and 27.7 """' as the amount 

 of the latter driven off. On repeating the experiment 

 with a somewhåt larger quantity of carbonate of smia. 

 earefully weighed ; -'14.1"""' were found to have been liber- 

 ated, whereas the exact proportion would have been 33.2"*» r . 

 i luring the process of boiling. the rluid at first continued 

 perHectly clear; hut after the dapse <>i' about half an hour 

 magnesia began to be precipitated, in- which with the 

 most delicate tests I failed to detect the smallest trace 

 of carbonic acid. According to H. Rose and other authors 

 basic carbonate of magnesia is to a considerable extent 

 soluble alike in water and in solutions of diVers salts. 

 so that small quantities give no precipitate: and hence 

 it is not surprising that with a solution so diluted as that 

 made use of for these experimeuts. the oxide should not 

 have been- precipitated before it bad given off all its -car- 

 bonic acid. 



. ■ If. sea-water be-boiled during concéntration. this 

 precipitation of magnesia may be easily ov.erlooked. since 

 it does not take place till after the lapse of soine time. 

 and the turbidness of the concentrated fluid might there- 

 tbre be ascribed to the deposit of gypsum. When the 

 water. too. is evaporated in an open dish. the precipitation 

 will be considerably retarded, since the carbonic acid es- 

 capes much more slowly in an atmosphere containing car- 

 bonic acid than in a current of air from which all car- 

 bonic acid has been expelled : and this accounts for' the 

 precipitation of magnesia in boiléd sea-water. so far as 

 I am aware. not having been previously observed. except 

 at least by Usiglio, 1 who detected the presence of free 

 magnesia in the dried residue. When. however. sea-water 

 is boiled without being concentrated in an atmosphere 

 .free from carbonic acid. and. with the cooler inverted. which 

 it easily may be with Glassens apparatus. the phenomenon 

 appears with great distinctness. as is the case on boiling 

 a mixture of soda and EpsOm salts; for after about half 

 an hour's boiling a precipitate begins to form. consisting 

 of pure magnesia, with no admixture of .lime and carbonic 

 acid and a trace only of • silicic acid. the latter arising 

 from the glass vessel employed in -the operation. If the 

 carbonic acid be simultaneously collected and deterniined. 

 the readiness with which it escapes is found to depend 

 not so much on the degree of concéntration as on the 

 duration of the boiling-process. about 2 hours proving 

 ainply sufticient to obtain a fluid free from the smallest 

 trace of carbonic acid. 



From what has been stated, there is. we think. con- 

 clusive proof, that the property possessed by sea-water of 



1 Journ. tur pract. Chem. 46 — 106. 



1 Journ. fur prac( Chem. l'i. p. 1' 



