Chemistry. - "The t1'ue speciftc !teat of salt-solutions. Cadmium iodiele, ammonium nitmte and zinc sulphate." By Prof. ERNST COHEN, DI". W. D. HELDElfl\fAN and Dl'. A. L. TH. MOF..8VELD.

(Communicated at the meetinR of May 3, 19!4).

1. In . the cOllrse of diffel'ent investigations we came to the con­clusion that it was necessary to detel'filine with great accuracy the true specific heat of solulions of cadmium iodide, ammonium nitrate, and zinc slliphate in different concentrations. As t.he figm·es relating to it are not to be fOlllld in the Iitel'atnre 1) ther al'e given is t.his papel'.

2. FOI' the detel'mination of Ihe values desired we have Ilsed t.he adinbatic electrical calorimetel· described in a formel' paper by ERNST COHEN and A. L. TH. MOESVELD I), which enabled us to delel'mine the dates in qlleslion with an acclll"aey of 0.5°/. u• FOI' all the pal·tic­ulars concerning t.he experimental pal't and the computations of the obsel'vations we refer to this paper.

A. Cadmium iodide solutions. (Temp. 19° C.)

3. The necessary solutions were prepared by dillIting a concentrated solution . The CdJ, nsed, was obtained from pure cadmium (soocalled "Kadmium KAHLBAUM", impurities 0,005'/,) and pure iodine, as described in a former papel' I). The cOllcenlration of the solutions obtained in this man nel' was conll'olled by determining lhe specific volume at 30°.00 C. This was possible by Ilsing the equation fOI'm­erly fOllnd 4) :

(VC)SOD.OO = 1.00435-0.802924 c + 0.016857 ct, which gives the specific volume at th at temperat.ure as a function of the concentration (grams CdJ, pel' 100 grammes of solution).

1) The figures mentioned in lhe literature, referring to the salts invesligated by us always indicate the meun specific heats within wide temperature intervals. As these intervals in our determinations were not greater than 6 ueRrees, we may consider thc figurel Cound as true specific heats.

s, These Proceedings 28,883 (1919-1920); Zeilschr. f physik. Chemie 96, 305 (1920); 100, 151 (1922) .

• ) ERNST COHEN and H. R. BRUINS, Zeitsch\'. f. physik. Chemie 96, 43 (1918), ') ERNST COHEN, C. W, G. HETTERSCHIJ and A, L. TH.. MOEsvELD, Zeitschr, f.

physik. Chemie 94, 210 (1920).

TABLE I.

True Specific Heat of Cadmium iodide solutions of different concentrations.

Temp. 19° C. .., ~

Average I Weight of Concentration deviation of Correct ion Specific Spec. heat Spec. heat Spec. heat Spec. heat Spec. heat

of the solution (vc}3O".OO

gr. of salt in the temp. of for heat of the solution calculated calculated calculated calculated 100 gr. of the calorim· solution found (1) -found (2)-found

in gr. lolution eter from tbe radiation found average (1) X 104 (1) X 104 surrouodings

I I

I I water

I I equivalent water· 850 .0(water) - - -0.025 +0 .0035 36.52 equivalent

Q..1f:I. ~ . C': ~ ~ Q..~ _r::T 0 (ti

<: -~ C': ~

= 0

= :::l

5 -P' S· 00

850.0 - - -0.017 +°.0025 36.40 36.40 (0 .9992) - - - :;. 850.0 - - -0 .010 +0 .001 4 36.31

~ .., I»

1320 .0 0.64394 44.30 - 0.004 +0.001 0.5879 I

I

0.5877 0.5868 -9 0.5877 ±O 1320.0 0.64394 44.30 -0.005 +0 .001 0.5875

I

en -.... (IJ ~

0 ~

'::f" CT)

~

1190.0 0.71587 I 35.41 I -0.009 1+0 .001 0.6697 0.6697 0.6715 +18 0.6696 -1

lllX>.O 0 .71587 I

35.41 I

+0.005 1-0 .001 0 .6696 I

S· ~ Q..

>--1103.0 0.77411 28.21 +0.012 -0.002 0 .7374 I 0 .7378 0.7394 +16 0.7380 +2 1103.0 0.77411 28 .21 -0.002 0.000 0.7382

I 986.0 0 .86194 17.41 +0.053 -0.008 0.8407

0.8410 0.8401 -9 0.8408 -2 986.0 0.86194 17.41 -0.006 +0 .001 0 .8413

-=-I»

~ CD

€ ;:. :::l

(JQ rij

~

910.0 0.93527 8.43 0.000 I 0.000 0.9247 I» .., I»

I +0.001 0 .9250 0.9925 -25 0.9248 -2

910.0 0.93527 8.43 -0.004 0.9253

567

5. F"om the val nes in the fonrth and eighth ('oillmns we have calculated by the method of least squal'es an equatioll of the second degree, which shows the relation between concentration and specific heat:

Wc = 0.9992-0.009033 c-0.00000625 C' . (1)

It gives however ditferences which al'e greater thall the experim­ental elTors. The equation of the thi"d degree:

Wc = 0.9992-0.0085097 c--"':"'0.0000424 c' + 0.00000056 c' (2)

on the contral'y cO"I'esponds exaclly wilh the "esnlls, as is seen from colulIlns 8 and 12 in table I.

B. Solutions of Ammonium uitmte (Temp. 32°.3 C.).

6. As the investigatiolls in which t.lle specific heat of these solutions plays a pari had 10 be made at 32°.3 C. (transitioll point of the modification III into IV), the 8pecitic heats of the solutiolls were also delermined at this temperature 1).

7. We started with a preparation which had been obtained by crystallizing an al ready rather pure pl'epal'ation from water. After cl'ystallization impurities could nol be found in 3 gl', of the salt .. The salt was completely dl'y, as was proved by duplieate detel'minations of the dellsity at 32°.3 C., whieh are in complete agreement with earlier investigations 1).

8. First of all we determined tlle curve which represents the specific volume of ammoniullJ uih'ate solutions as a fuuction of tbe concentration (at 32°.3 C.). ~'or Ihis pllrpose the specitie volume was determined of soilltions which had been prepared by weighing in salt and watel'. The pycnometer we used was all instl"UlIlent as devised by SPRENGKJ"ÛSTWALD·EYKMAN ').

Table II contains the resuIts.

9. By means of the method of least squares we find from these observations :

(Vc)a2.o3 = 1.00507-0.00392087 c + + 0.0000051003 c'-O.00000000566 C'. (a)

Table 2, columns 5, 6 and 7. shows the agreement between the values calculated and the values found for Vc.

I) ERNST COHEN and J. Kooy, These Proceedings 32, 94.3 (1924); Zeitschr. f. physik. Chemie 109, 81 (1 U24) .

I) Recueil des Trav. Chim. des Pays.Bas 18, 24 (1894.).

568

TA B ·L E 11.

Specific Volume of solutions of Ammonium nitrate of different concentrations.

Temp. 32°.3 C .

. -- " .

· !F Weight Weight of .SU: vC calculat-!~ ~5 vc aver&ge vc calcul-- '" .-of salt solution c Ol 0 'Ei t'c found ed-found

in gr. in gr. ~o~ö found ated X 10' c. Ol o .. ü'Qll

3.8536 38.4570 10.01 0.96628 0.96628 0.96633 +5

3.8536 38.4570 10.01 0.96627

4.8339 24.1098 20.05 0.92838 0.92839 0.92844 +5

4.8339 24.1098 20.05 0.92839

7.6877 I 25.5763 30.08 I 0.89164

125.5763 1 0.89165 0.89165 0.89158 -7

7.6877 30.08

9.7456 24.3950 ·1 39.95 0.85628

24 .3950 1 0.85630 0.85621 -9

9.7456 39.95 0.85631

11.8383 23.7670 49.81

1

082166 0.82161 0.82173 +6

11.8383 23.7670 49.81 0.82167

14.2543 I 59.52 0.78848 0.788551 1

23.94 .. 0.78850 +5

14.2543 23.9459 59.52 0.78852 I

15.7044 22 .5557 1

69.62 0.75494 I 0.754891 0.75492 -3

15.7044 22.5557 I

69.62 0.75489 I

I I

10. The cOllcentl'ation of the solntions whose specitic heat was measured, was obtained with the equation (a) by detel'mining the specific volume at 32°.3 C. and calculating c.

11. In table IJl we gi,'e the results of the calol'imetric detel'minalions.

12. By the method of least squares we find fol' tbe l'elation between the specific heat (wc) and the concentl'ation (c) of the solntions:

(wc) 320.3 = 0.9~85-0.00765857 c + + 0.000030811 c'-0.000OO006473 r l

,

569

TA BLE lIl. True Specific Heal of solulions of Ammonium nilrale of diffrrenl concenlralions.

Temp. 32°.3.

Cl -'- , Cl ; 5 ;g~ _ Cl

i I~ Weighl ·g.Eë Cl o O~O Ol 0

Specific ~CI • §O Cl 0

l';~ 4,).- •

J'~] of 0 ''::: ..c:-" ..c~-volume

f! _ .0 e.2 ~ e Cl

'::: . ::I " u~X lolulion ä ëä ~ '; u '-0' Jr~ § ~~~ ~O.!! at 32°.3 :.! ~ :; ': ~1lo .;:;01

in ,," - '2 J J3 'ü ,,~ '0: e '211 ~ ~g ~ .. .. Vc <> • ...., 8 .. "..c Cl "..c-

grammes 0""'- " " ., Cl p,- P, - ::! ~= 5 ~3.§ ~ -!3 -S '- .B 00'- u.J'öJa 0 ° 0

1133 .09 0.75548 69.46 -0 .022 +0.003 0.5931 I 0.5935

0 .5935

1 0

1131.31 0 .75548 69.46 -0.009 +0.001 0.5939

1076. "1°.78257 61.31 +0.018 -0.003 0.6298 0.6297 0.6298 +1

1078.33 0.78251 61.31 +0.011 -0.Q02 0.6295

1036 .96 0.82088 50 .03 +0.041 -O.OOG 0.6844 0.6847 0.6844 -3

1038 .00 0.82088 50.0.3 +0.015 -0.002 0 .6850

996 . 10 0.85589 40.06 -0.009 1+0.001 0.1316

. +0.053/-0.001 0.7379 0.7370 -9

996.58 0.85589 40.06 0 .1381

951.51 0 .89115 30.03 1 -0.025 +0.003 0.7932

/

0.7931 0.7945 +14 958.13 0 .89175 30.03 +0.001 +0.000 0.7930

915.99 0.93155 19.22 -0 .010 +0.001 0.8622 0 .8620 0.8622 +2

914.89 0.93155 19 .22 -0.015 +0 .002 0.8618

868.25 0.96624 10.03 -0.002 0.000 0.9250 0.9254 0.9247 -7

871.65 0 .96624 10.03 --0.004 0.000 0.9258

FrOllt the <,olumns 6, 7 and 8 of tabel lIJ we !lee Ihe good agl'ee­ment oetween 'he valnes given oy the equfltion alld tlle l'esllits of Ihe meaSlll'emenls.

C. Zinc .\'1.tlphate solutions (Temp. 19° C.).

13. The salt was pl'epared by crystallizing an already l'athel' pme

preparllotion. By weighillg we made a solutioll of34.21 '/. (gl·. ZnS0 4

in 100 gl'. of solnlion) and conlrolled ,he ('ompositioll by g/'avi­mell'Ïe allalysis, according 1011Ie method of EUl.EH 1). Fl'om this

1) Zeitschr. r. anorg. Chemie 26, 14,6 (1900). 37

Proceeciings Royal Acad . Amsterdam. Vol · XXVII.

570

standaJ'd soilltion WeJ'e pr'epared ot,hers. whose concent,r'ation was 1/4' 1/ •• 1/4' I/S and 1/16 of lire original solulion. Ille cOllIposition ofthe sollltioriS 1/. and 1/4 beilIg eontrolled again hy allalysis, The specific volumes wel'e deter'mined 100 (at 30°,00 C.). They have also been il1seJ'ted in table IV wlrich cOlllaills the l'esults of the determinations of the specific heat,

TABLE IV.

True Specific Heat of Zinc lulphate solution. of different concentrationl.

Temp. 19° C.

c c ~ ;; Ol

-c::oo il~ .5!'- C 0 C .a'Ql) ... -_ _ . ° :s Ol .S! Ol ° .. lLg ~ uO"0 ca- .... - - C .Cl ~ ..c: 0:; u .a~

!:=~; ~.- ~ u :; C u :s :- u:s.! u~X ~ .. Co ~_oo Ol u " <J:: 0 :s <J::-" <J::-:S ~~~ ~ a .S!o

Ilo., .. 'ü J? .- ° .- ° u 1lo:S :;0' Col 00 e E'- 'QII ., u.,~

u __

C .... .. Ol 8.- " ... C 8..'ë) ~ u u Cl 000- 0

° .; ë ~ ~ ~o g Ilo- :s :-SlM U'Ql) 00 ° 00 oo~-S ...

0 5 . 148 ... ~ter 43.92 eqUIvalent

0 5.036 . 44 .06 - - - 1.00435

0 5 . 144 " 43. 98

1

1

34.21 5.139 0.6692 0.6688 0.6692 +4 0 .68960

34.21 5 . 166 0.6683

25 .66 5.148 0.7352 I 0.76222 0.7354 0.7346 -8 25 .66 5 . 146 0 .7356

I 17.14 5.156 0 .8112

0.8113 0.8113 ± 0 0 .83908 17 .14 5 . 148 0.8115

8.60 5.143 0.8989 I 0.91958 0.8989 0 .8992 + 3

8.60 5 . 136 0.8989 I

4.30 5.148 0.9472 / 0.9414 0.9478 +4 0.96124

4.30 5.145 0.9416 I

2 . 15 5 . 156 0 .9725 0.9724 0.9731 +7 0,98258

2 . 15 5 . 150 0 .9723

0 /5.147 w~ter 44.08/ -eqUIvalent

/

- - 1.00435

571

14. By means of the method of least squares we obtained from the values found for the specific heat:

Wc = 0.9992-1.290 c + 0.773 Cl

(sum c = 1).

From the columns 5, 6 alld 7 in tabla IV we find that there is good agl'eement between Ihis equatioJl and Ihe experimental resuIts.

SUMMARY.

Tlte true specific heat of solutiolls of different concentrations of cadmiulll iodide (at 19° C.), amlllonium IIÏlmte (at 32°.3 C.), and zillc sulphate (at 19° C.) was determined in an elect.·ical adiabatic calorimeter, with aD accuracy of 0.5 ' / •• .

Ut1'ecltt, April 1924. VAN 'T HOFF-Labomt01·Ïlçrn.

37*