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studied spicules wliicli liad l)een dried iu lliis way foi' some days 

 at an ordijiary temperature, and also in Victor Meyer's toluol bath 

 at 104°. The heating, however, had no influence on the aspect. 

 The determinatif>n of the refractive index is a little less accurate than 

 with ordinary spicules, because on drying the lamellar structure had 

 become somewhat more conspicuous, and therefore the disappearance 

 in glycerine is a little less perfect. Still \ve could determine in 

 jietroleum-benzijie the refractive index ??, = 1.4052— 1.4055 ; with 

 diluted glycerine the same results were obtained. 



Tf the dried spicules, mounted in glycerine with n = 1.4055, and 

 with the border of the coverglass well shut bv means of vaseline, 

 are left to themselves, gradually from the outside the refraction is 

 seen to increase, and after one day the spicules become again highly 

 refractive. If they are now as much as possible separated from 

 adhering glycerine and transferred iiito glycerine of ?i = 1.4508, it 

 is seen that they disappear in this medium, and consequently have 

 absorbed again their original quantity of water. Spicules, which have 

 been dried \)\ P^ 0. and are exposed to the air afterwards, behave 

 In the same way. (jn the other hand we have examined the behav- 

 iour of spicules which, after being isolated and washed, were not 

 dried in the air, but immediately after removing the adjacent water, 

 were mounted in glycerine with y^ = 1.4508. We could iiuleed see 

 a xQvy slight difference with spicules Avhich had been dried in the 

 air at an ordinary temperature, more than corresponded with |)Ossibly 

 adiierent water, but too small to bo measured. However, it ajtpears 

 that, even at the ordinary teuiperature, the spicopal gives otf 

 souje water. 



Consequently we have demonslrated tliat the spicopal is a form of 

 hydraled siliceous acid, which may gi\e oil' water in an atmosphere, 

 dried by P.,()., winch (Uuiinishes hereby in refractive index, and 

 which may again al)Sorb the oi-igiual quantity of water by immersion 

 in a water}' solution or by exposure to moist air. The spico})al also 

 behaves with regard to the absoi-ptive j)ower for water just as a 

 gel, as has been shown by the well known and intricate researches 

 of VAN Bemmelkn. 



(To hi> coiitniiii'dj. 



