32 



NEGRETTI AND ZAMBKA, HOLBORN VIADUCT, E.G., 



STANDARD THERMOMETERS. 



Two important improvements in the Tubes and Scales of Thermometers 

 and Barometers, first introduced by Negretti and Zambra, have become so 

 extensively used that N. and Z. deem a short notice necessary to secure to 

 themselves the credit of the inventions. 



The first improvement is the introduction of a white Enamel at the back of 

 Thermometer Tabes, which renders the mercury much more plainly visible 

 both in large and small-bore tubes. Most of the extremely delicate Ther- 

 mometers now in use would have been almost useless but for this enamelling. 

 This invention has also been applied to the back of Barometer Tubes. 

 The second invention is the use of Porcelain for Scales and Dials of 

 Thermometers, Barometers, &c., in place of metal, ivory, or wood, all of which 

 so soon become soiled and tarnished, and eventually the divisions and figures are 

 obliterated by the action of the atmosphere, sea-water, or damp. The divisions 

 and figures on these porcelain plates are etched in with fluoric acid, 

 and the colour permanently burnt or melted in by fire. 

 That these are important inventions may be inferred from 

 their use in all thermometers and barometers supplied to 

 the Board of Trade and other Government departments. 



38. Independent Standard Thermometer (fig 32), 

 with Negretti and Zambra's Enamelled tube, and Engine, 

 divided into either Fahrenheit or Centigrade scales, the 

 divisions engraved on its own stem and mounted on 

 silvered brass, boxwood, or Negretti and Zambra's 

 Patent Porcelain Scales. 



Price, 550 

 Kew Certificate for above Thermometer 050 



39. Comparative Standard Thermometers (fig. 33). 

 These Thermometers are made by comparison with great 

 care, from an accurate standard, correct to T V f a degree. 

 Engine-divided EnamelledTubes mounted on Silvered Brass 

 or Negretti and Zambra's Patent Porcelain Scales, with 

 Mahogany or Oak framing. Price, 220 and 2 10 



FIG. 32. 



N. & Z's Standard Thermometers are made from selected tubes, the internal 

 diameter of which is ascertained by very carefully conducted experiments. They rr T( -, oo 

 'J are also strictly tested for index error, and a copy of the corrections, if any, 

 furnished with each instrument, if required. 



We recommend the Standard Thermometers not to be mounted in any way, 

 but the tube to be enclosed in a strong outer glass jacket; the bulb dipping 



