4-30 Mr, Prideaux's Continuation of the Table of Atomic Weights, 



of some artifice in the manufactory, for commercial advan- 

 tage, and are therefore neglected. 



(7i.) Selenic. — Discovered by Sertuerner, since the publica- 

 tion of Thomson's book. 



(o.) Silica. — See note on Silicon. 



(p.) Tartaric. — Berzelius's number contains 5 volumes, or 

 2 1 atoms (according to our system) of hydrogen. The ana- 

 lyses of Thomson and Prout coincide in giving it 2 atoms, 

 which is therefore regarded as its true composition. The 

 augmentation in the third column is due to carbon. — See 

 note (b). 



(q.) Tungstic. — See note on Tungsten. 



Having now submitted to the correction of your readers 

 the leading equivalents, leaving the bulk to be seen on the 

 scale itself, I wish to add a short notice of what is distinctive 

 in the construction of the instrument. 



The object was, to contain in portable compass, of easy re- 

 ference, and subject to the sliding scale, all the salts and pre- 

 cipitates used in practical chemistry, and their secondary and 

 elementary components; multiples of the elementary atoms 

 occurring in vegetable and animal analysis, and of water ; and 

 to present at one view a general table of atomic weights, sim- 

 ple and compound, referable by moving the slider, to either 

 the hydrogen or oxygen scale. 



The symbols of Berzelius offered the compactness and faci- 

 lity of arrangement, which were the first requisites, with the 

 further advantage of exhibiting the atomic construction of 

 every substance contained; a point of some importance, as 

 will presently appear, in apportioning compound salts, and 

 convenient in looking out the ingredients of complicated sub- 

 stances, as phosphoric and hydrocyanic acids. Their defi- 

 ciency, for our present purpose, was in conspicuity, which 

 I have endeavoured to supply as follows : 



Where many of the symbols had the same initial, the Eng- 

 lish is substituted in some of them for the Latin one: as T, 

 tin; An, antimony; for Su, stannum; St, stibium ; &c. &c. 

 as explained in an index-table attached to the scale. Acids 

 and negative bodies are distinguished by upright letters, the 



others being inclined ; as S sulphuric acid, CI chlorine, Po 

 potash, H hydrogen ; and Salts by combination of the upright 



and inclined symbols, as PoS sulphate of potash, AgN nitrate 

 of silver. Water (Aq, in running hand) attached to any 

 symbol, shows it to be a hydrate, and generally crystallized; 



