190 NEGRETTI AND ZAMBRA, HOLBORN VIADUCT, E.G., 



624 Spirit Gravity Beads are small light hollow spheres made of white or coloured glass 

 about half-an-inch in diameter, with a stem or tail of about a quarter of an inch in length. 

 The use of this stem is for adjusting each bead to a certain degree of Specific Gravity, or 

 to a given degree of Sike's Hydrometer Scale. The degrees are engraved upon each Bead, 

 thus forming them into rough Hydrometers for ascertaining the Gravity of various Fluids of 

 Spirits. When the Bead floats about half-way in any sample of liquid to be tested, the 

 density or specific gravity of such liquid is indicated by the figures or numbers engraved 

 upon the bubble. 



525 Salt Water Beads, or bubbles, for Aquaria . . . in pairs 020 



The average Specific Gravity of Sea Water is T026 to 1/028. 



Gravity Beads for Aquaria are made of different coloured glass, one adjusted to float 

 upon the surface of the water, and the other to remain at the bottom of the tank when the 

 water is of suitable density for the healthy growth of fish or plants. 



Each. 

 s. d. 



526 Specific Gravity Beads, (or Spirit Bubbles, Glasgow 



Beads), for showing the strength of spirits, 



set of twelve, in japanned tin box .... 066 



527 Ditto, ditto . . . . set of eighteen 10 6 



528 Specific Gravity Beads, for heavy and! light fluids, such 



as aether, alcohol, ammonia, oil, naphtha, acids, each . 010 



529 Specific Gravity Bottles, 1,000 grains' capacity, in tin case 



with counterpoise weight. (See also Chemical Section.) 10 6 



530 Ditto ditto 500 grains 086 



531 Ditto ditto 250 grains 066 



532 Nicholson's Gravimeter, for ascertaining the specific 



gravity of metals or other solid substances, 



Japanned tin (fig. 532) with Metal Case ... 10 



533 Nicholson's Gravimeter, larger size, accurately made in 



BRASS, fitted in case, with weights ranging from l-10th 



to 1,000 grains (fig. 533) .... 330 



Nicholson's Hydrometer or Gravimeter is a modification 

 of Fahrenheit's instrument, and is made either of very light tin 

 japanned, or gilt brass ; its form will be seen in fig. 532. A 

 mark is made on the stem supporting the cup to which the 

 instrument is adjusted by weight to float in water. The weight 

 of the loaded instrument when sunk to this point is the weight 

 of the volume of liquid displaced by it. It gives, therefore, the 

 relative weights of equal volumes of the liquids into which it is 

 placed. The Gravimeter is usually made to displace 3,000 or 

 4,000 grains of water, and is sensible to the tenth of a grain in 

 this quantity. With this instrument the 'specific gravity of 

 ...,., solids may also be ascertained. By placing the solid to be tested 



IG * ifilllpl in the cup on the top of the stem and adjusting the additional 



weights required to sink the Hydrometer, the weight of such 

 solid body in air is found. Then by placing the solid in the 

 lower cup immersed in the water, and again adjusting the 

 weights as before, the weight of the solid in water is ascertained; 



F 533 ^ and f rom tliese two resuits tne specific gravity is calculated. 



