STORAGE BOTTLES 33 



further examination, and the kind of storage bottle 

 is of considerable importance. If the examination is 

 to be confined to a determination of the chlorine by 

 chemical methods and of the specific gravity by 

 weighing, a sample of 150 c.c. will be sufficient ; 

 larger quantities are of course more convenient, but, 

 if many samples are to be collected, the size of the 

 bottles is a serious consideration. One of the writers 

 uses bottles known in the trade as " 6-ounce milk 

 bottles with porcelain stopper, rubber washer, and 

 swing catch," holding about 170 c.c. These are very 

 convenient in use and comparatively cheap. Each 

 batch should be carefully examined when received 

 from the makers, and any in which the washer appears 

 to fit loosely should be rejected. For the washers 

 nothing but the best Para rubber should be used ; if 

 there is any difficulty in obtaining them from the glass 

 makers, they may be had from reliable dealers in 

 chemical apparatus. All glass is slightly soluble in 

 water on long standing ; the brown variety, used for 

 beer bottles, seems to be less affected than other kinds. 

 With good glass this solubility diminishes with use, 

 and bottles that have been used for sea water pre- 

 viously are always to be preferred. New bottles may 

 be improved by steaming, followed by washing with 

 hot water. For all ordinary hydrographic purposes 

 it may be said that the solubility of the glass will not 

 affect the determination of the chlorine by volu- 

 metric methods ; but the specific gravity becomes 

 noticeably higher with time. When the greatest 

 accuracy is required it would be advisable to use 

 bottles of Jena glass ; these are to be had in sizes rang- 

 ing from 250 c.c. to 2,000 c.c. ; they have ground-glass 

 stoppers, which should be replaced by india-rubber. 

 The price, however, would be rather high. 



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