70 



MARINE BOTTOM SAMPLES OF LAST CRUISE OF CARNEGIE 



entirely of manganese nodules. Gibson (1891) was unable 

 to find any bismuth in his famous analysis of manganese 

 nodules from Challenger station 285, which is about 1000 

 miles southeast of Carnegie station 86 where sample 46 

 was collected. 



Samples 6 and 8 in the Atlantic, and samples 27, 30, 

 40, 81, and 89 in the Pacific contain tin, and this element 

 is possibly present also in sample 46. Of these sam- 

 ples, six are classified as Globigerina oozes, one as a 

 red clay from the south Pacific, and one (sample 89) as 

 a calcareous beach sand from Easter Island. No evi- 

 dence of tin could be detected in sea water by Orton and 

 it has not been detected previously in marine bottom de- 

 posits. Orton, however, reports the blood cell of the oys- 

 ter as containing about 0.05 per cent tin. Goldschmidt 

 (1933) believes that tin should be found as the oxide in 

 the insoluble residues of hydrolytic decomposition, 

 namely clays and silica. 



In samples 6, 30, 40, and 89 zinc also is recorded as 



possibly or doubtfully present, that is in quantities less 

 than about 0.05 and possibly greater than 0.01 per cent. 

 Clarke and Steiger record 0.0052 per cent of zinc in 

 their analysis of a composite sample of fifty -one red 

 clays dredged by the Challenger and 0.001 per cent in a 

 composite sample of fifty-two terrigenous clays. Bodan- 

 sky (1920), Orton (1924), and Goldschmidt (1933) report 

 less than 0.1 mg per kilo of the same element in sea 

 water. Bodansky, however, found from 0.0025 grams to 

 0.341 grams per kg in the ashed tissues of twenty marine 

 animals and concluded that it is a normal constituent of 

 the tissues of these forms. According to Thompson and 

 Robinson (1932) zinc has been detected in the ashes of 

 some sea plants, the ashes of Zostera maritima showing 

 0.035 per cent. It seems possible, therefore, that the 

 zinc in bottom deposits is the product of the decomposi- 

 tion of marine plants and animals. According to Gold- 

 schmidt, however, zinc is associated with iron and man- 

 ganese hydroxides. 



GRAIN DENSITIES, WEIGHT-HUMIDITY AND WEIGHT-TEMPERATURE RELATIONS 

 OF CARNEGIE PACIFIC BOTTOM SAMPLES 



P. G. Nutting 

 United States Geological Survey 



Grain Densities 



The mean grain densities of the samples sufficient in 

 quantity for the determination are as follows: 



Table 20. Mean grain densities of certain samples 



Densities were determined by first grinding the 

 room-dry sample to pass a 300-mesh sieve (50 microns) 

 then drying at 160° C for 24 hours and cooling in a P2O5 

 desiccator. Tetralin (tetrahydronapthalin) was used as 

 pycnometer fluid because of its excellent wetting power 

 for minerals. Fine grinding facilitated the expulsion of 

 air. After weighing in an ordinary 5-cc pycnometer, the 

 clay was wet with tetralin and shaken with it at intervals 

 for 24 hours, then the density determination was com- 

 pleted. 



Blank experiments with quartz, both coarsely broken 

 and ground to 50 microns, indicate that the error due to 

 adsorbed air and moisture is less than 0.1 per cent when 

 using the aboVe procedure. The adsorption of tetralin on 

 this class of clay is very slight and produces an error of 

 probably less than 0.25 per cent in the densities, though 

 no method has yet been found for accurately determining 

 it. 



Dehydration at 160° C removes sorbed moisture and 

 gases rather completely without breaking down hydrates 

 or carbonates. Organic structural material such as cel- 

 lulose is but slightly affected. Oxidation is only slightly 

 promoted. The densities of this class of clays, when 

 dehydrated at 160° C, are at or near their maxima. 

 Similar tests on a brown clay soil gave 2.428 room dry, 

 30 per cent humidity, 2.650 after 24 hours at 160°, and 

 2.405 after ignition at 800° C in air. 



Weight -Humidity Relations 



The samples were ground to pass a 150-mesh sieve 

 (0.1 mm) and placed in thin layers in glass dishes in des- 

 iccators containing sulphuric acid solutions having eight 

 vapor pressures ranging from 5 to 95 per cent saturated. 

 The initial treatment consisted of drying the samples 

 for two weeks over P2O5 (zero humidity) to give the 

 base weight. Temperatures during the experiments var- 

 ied little from 27°.0 C. About 95 per cent of the change 

 in weight is attained in 24 hours under these conditions, 

 but in all cases at least two weeks was allowed for com- 

 plete equilibrium to be attained. The weights tabulated 

 below (table 21) are relative to those at zero humidity. 



At low moisture contents the vapor pressures of 

 these samples do not differ greatly from the average for 

 ordinary clays (cf. P. G. Nutting, "The adsorbent clays" 

 Bull. 928-C fU.S.G.S.] in press). Further, the percent- 

 age increase in vapor pressure is directly proportional 

 to the percentage increase in moisture content of the 

 sample throughout the lower range of humidities. 



At higher vapor pressures approaching saturations, 

 these samples show the properties of hygroscopic salts 

 rather than of definite hydrates as all curves turn steep- 

 ly upward at the highest humidites. If such hydrates as 

 phillipsite, for example, were present each curve would 

 approach a definite maximum as do the curves for the 

 simple oxides Si02, AI2O3, and Fe203 (ibid). The en- 

 ergies of association of water with moist clay when such 



