66 RAY: THE MOLECULAR VOLUMES OF THE NITRITES OF

1X.-The Molecular Vo Zumes of the Nit rit cs Barium, Styontium, and Calcium. By PRAFULLA CHANDRA RLXy.

IN continuation of my previous investigation (Trans., 19OS, 93, 997), the determination of the molecular volumes of the nitrites of barium, strontium, and calcium has been undertaken. As these nitrites crystallise with one molecule of water, two sets of results have been obtained, namely, those of the hydrated and of the anhydrous compounds. Incidentally, the molecular volumes of the water of crystallisation of a class of well-defined monohydrated salts have also been ascertained.

The preparation of these nitrites has already been described (Trans. , 1905, 87, 178). It is only necessary to add here that, owing to the deliquescent nature of these salts, special precautions were taken in handling them. Calcium nitrite caused great trouble in the damp climate of Calcutta. Although this salt was quickly pressed between folds of bibulous paper to remove adhering mother liquor, it always gave a variable and much higher percentage of water than that required by theory. After several unsuccessful trials, the following method gave satisfactory results :

The substance, dried as above, was placed overnight in a desiccator containing sulphuric acid of sp. gr. 1.625. Barium nitrite under similar treatment also yielded the monohydrated salt. The salts were de- hydrated a t 108-110O. Calcium nitrite, when dried a t llOo, proved t o be faintly alkaline, but the estimation of nitrogen agreed with the theoretical value.

Barium Nitrite.-Three distinct preparations gave H20 = 7.67, 7.70, and 7-50 respectively. Ba(N0,),,H20 requires H,O = 7.29 per cent. The anhydrous salt gave Ba=59-S2, the calculated amount being 59.83 per cent, It may be mentioned here that A.rndt stated that, even a t llOo, barium nitrite is not readily dehydrated (Zeitsch. anorg. Chem., 1907, 27, 355). The specific gravity of the hydrated salt was found to be 3.185 at 2 7 O ; that of a second preparation was 3.162 a t

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BARIUM, STRONTLUM, AND CA.LCIUM. 67

31°, the mean value being 3.173. The specific gravity of the anhydrous salt was 3.232 at 23O; a second preparation gave 3.228 at 23'; mean =3*23. Slight variations in the degree of hydration olten cause considerable disparity in the value.

Strontium Nitrite.-The percentage of strontium in the monohydrated salt mas 44.06, the calculated amount being 44-95. The mean of two fairly concordant determinations of the hydrated salt gave 2.645 at 27" as the specific gravity, whilst that of the anhydrous salt was 2.S67.

Calcium Nitrite.-The estimation of water in several samples gave H,O= 11.97, 11-55, 1 !*SO, and 12.50. Ca(lY0J2,H,O requires H,O= 12.00 per cent. The specific gravities of two distinct preparations of the hydrated salts were found to be 2,225 and 2.237 respectively at 34"; mean=2*231. The specific gravities of two samples of the anhydrous salt were 2.286 and 2.302 ; mean = 2.294. The molecular volumes of the salts * calculated from their specific gravity determinn- tions are presented below in a tabulated form :

Name of salt. Mol. wt. sp. gr. 1101. vol. Ba(NO,),,H,O ............... 247 3.173 77-87 Ba(NO,), .................... 229 3-230 70.90

Diff. (mol. VOI. of H,O) ........... 6'97

S r (NO,),,H,O .............. 197.3 2.645 74.59 Sr(NO,),. ....................... 179.3 2.867 62-54

Diff. (mol. vol. of H,O) ............ 12-05

Caf H,O ............... 150 2.231 67.24 Ca(NOJ2 ................. 132 2'294 57-56

-- Diff. (mol. vol. of H,O) ............ 9-68

It is evident that the unlike the anhydrous molecular volumes, but the atomic weights of

above nitrites, even in t,he anhydrous state, magnesium sulphates, have not identical the latter values appear to be functions of the corresponding element. The molecular

volume of the water of crystallisation also varies, being least i n barium nitrite and greatest in strontium nitrite. This is no doubt due to the fact that the water molecules are held with varying degrees of tenacity in the three compounds. According to Kopp's conclusion, however, in salts containing only a small number of water molecules (1 to 3), the molecular volume is a constant number, namely, 12.4.

If the molecular volumes of the nitrites are deducted from the

* Magnesium nitrite could not be included in this series as the salt crystallises with three molecules of water, and when it is kept in a vacuum over sulphuric acid, i t parts with only one niolecule (compare Ray, Trans., Zoc. cit., 779).

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68 MOLECULAR VOLUMES OF NITRITES

corresponding volumes of the nitrates, the remainder is approximately constant. Potassium and sodium nitrites have been left out of con- sideration as their molecular volumes are abnormal, as pointed out iu the previous paper (Eoc. c i t . , 1000). Thus :

Salt. Mol. vol. Diff. (for OJ. Diff. (for 0). .............. Ba( NO,),. ;;:;* 1 9.9 4.95 Ba( N02)2”. ............

Sr(N03) , 70”Jl 7 Sr(N02), ............... 62.54 J Ca( NO,),.

............... 8.37 4-19

8 *04 4-02 .............. Ca( NO,), ..............

............ 8-92 4 ‘46 Mean ............ 4 *40

(AgNO,), 78-08 (AgNO,), ............ 69’16 }

According t o Kopp the radicle NO, occupies a constant volume, namely, 38.6, in the nitrates of barium, strontium, silver, potassium, and sodium (Thorpe, Eopp Mentorial Zecture, Trans., 1893, 63, SOO). It may safely be assumed that calcium nitrate also comes under this category.

As it has just been shown that the increments in volume due to the accession of an atom of oxygen are approximately constant ( = 4*4), we get 28.6 - 4.4 = 24.2 as the average volume of the radicle OF the nitrite, NO,, of these metals. As earlyas 1840, Kopp pointed out that in the salbs of the metals of the alkalis and alkaline earths, the “primitive atomic volumes” of the metals are not retained, although in the com- pounds of the heavy metals, for example, silver and mercury, the latter retain their original volumes. If we deduct from the molecular volumes of the nitrates the constant 28.6, me get the following values for the atoms of the respective metals : B3a = 23.60, Sr = ’13.71, Ca = 8.40, and Ag = 10.44.

Now the original atomic volumes of barium, strontium, and calcium are 36.5, 34.9, and 25.4 respectively. One cannot help being struck with the fact that the latter bear a simple proportion t o the lormer. Thus barium in its compounds occupies two-thirds the original atomic volume, whilst strontium and calcium occupy nearly one-third of the same. Considering the difficulties in the way of preparing these metals in the pure shape, closer approximation cannot be expected. The radicle NO, in the liquid condition has the volume 32.0 (Thorpe,

* The molecular volumes have been calculated from the specific gravities as given in Erdmann-Kothner’s iVatur-Ko?zstarhm, 1905. Although the authors give no reference to the names of the observers, they have evidently placed greater reliance on the determinations by Favre and Valson (Compt. rend., 1873, 77, 802) than on those by Pilhol. The specific gravities as found by the latter are often too low. Thus, the specific gravity of Ca(NO,), is given as 2.0, whereas, according to Favre and Valson, it is 2’5. Filhol’s number is untrustworthy on the face of it,

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ORGANIC DERIVATIVES OF SILICON. PART IX. 69

Trans., 1880, 37, 382). We have seen above that in the nitrites of the alkaline earths and of silver, the radicle NO, occupies the volume 24.2, or almost exactly three-fourths of the former, Prideaux has recently shown that the atomic volume of liquid phosphorus is 20.0, whilst in the case of quinquevalent and tervalent phosphorus the values are 15.10 and 25.06 respectively (Trans., 1907, 91, 1715). Here, also, a very simple relationship is noticeable. It is scarcely probabIe that so many striking coincidences should be purely acci- dental. An interesting problem suggestive of a law of proportionality seems to be opened up. Indeed, the assumptions made by Schroder, Hermann (J. p r . Chem., 1876, [ii], 13, ZS), and E. Wilson (Proc. Roy. Soc., 1881, 32, 457) need a careful reconsideration.

CHEMICAL LABORATORY, PRESIDEXCY COLLEGE,

CALCUTTA.

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