594 Mr. J. Y. Buchanan on Chemical Work 



nected by a straight rod, so that they are simultaneously either open or 

 shut, or at least at the same phase of being open or shut. When water 

 is to be collected by its means, the stopcocks are opened and the instru- 

 ment sunk to the required depth, having been previously securely 

 fastened to a sounding-line. The operation of sinking must be carried 

 on without a check, owing to the peculiarity of the closing-apparatus. 

 When the required depth has been reached, the line is checked, hauled in 

 a few fathoms, let go again, and finally brought to the surface by means 

 of a donkey-engine. The rod connecting the stopcocks is furnished with 

 a metal plate, which, during the descent, is retained in a vertical position 

 by the passage of the water on both sides of it. When, however, the 

 direction of motion is reversed, the plate falls down into a horizontal 

 position, when, by its passage through the water, it exercises such a 

 downward pressure on the rod that the stopcocks are closed. Arrived 

 at the surface, it contains the water which it had enclosed at the depth 

 in question. A small safety-valve allows of the escape of the surplus 

 water, which, owing to the greater density of the water below the sur- 

 face, it has enclosed in excess of what it can hold at atmospheric tem- 

 perature and pressure. The apertures of the stopcocks being necessarily 

 smaller than the diameter of the cylinder, the efficiency of the instrument 

 in really changing the water as it descends was tested before leaving 

 England in a freshwater lake, the water with which it was filled at the 

 surface containing some yellow prussiate of potash. It was found that 

 the water fetched, under these circumstances, from depths over lj 

 fathom was unacted upon by solution of perchloride of iron. The rate, 

 therefore, of change of water is satisfactory, as we can be certain of 

 obtaining an average sample of the last two fathoms passed through 

 by the instrument. 



Eepresenting the specific gravity of distilled water at 4° C. by 100,000, 

 I found that of ocean water at 15°*56 C. to vary between the ex- 

 tremes of 102780 and 102400 ; so that, to be of any value at all, the 

 possible error in the results must not exceed 10. The hydrometer used 

 for these observations is fully described in the paper above referred to. 

 Its description is briefly as follows : — 



The stem, which carries a millimetre-scale 10 centimetres long, has 

 an outside diameter of about 3 millimetres, the external volume of the 

 divided portion being 0*8607 cubic centimetre; the mean volume of the 

 body is 160*15 cubic centimetres, and the weight of the glass instrument 

 is 160*0405 grammes. With this volume and weight it floats in distilled 

 water of 16° C, at about the lowest division (100) of the scale. In order 

 to make it serviceable for heavier waters, a small brass table is made to 

 rest on the top of the stem, of such a weight that it depresses the 

 instrument in distilled water of 16° 0. to about the topmost division (0) 

 of the scale. By means of a series of six weights, multiples by 1, 2, 

 3, 4, 5, and 6 of the weight of the table, specific gravities between 



