S N O 



SOD 



named^yfAVon. Little is known, however, of the nature of 

 this fubllance, except that it is dark -coloured, and will bear 

 a conliderable heat without undergoing change, and that it 

 decompofes water, and is converted into fdica when brought 

 in contact with that fluid. It is alfo capable of combining 

 with iron, and probably other metals. Dr. Thomfon efli- 

 mates the weight of the atom of filicon, from the experi- 

 ments of Berzelius and Stromeyer above-mentioned, at lo, 

 and of fdica at 20. The fame chemift alfo confiders filicon 

 to be an acid, and propofes for it the name oiflicic acid, 

 in which cafe its compounds muft be denominated_/(/zVa/«. 



SILVER, in Cbemijlry. Dr. Thomfon, from the moil 

 recent experiments on this metal and its falls, ellimatcs the 

 weight of its atom at 137.5, that of oxygen being 10. See 

 Atomic Theory. 



SiLVEK 0;-«. See Silver, and Mineralogy, yfJ^/i'n^fi. 



SILURES, col. 2, 1. 32, r. Wiflc or Uflc. 



SIMIA Fatuellus, 1. i, for tallies r. long-tailed. 



SITACA. Add — twelve geographical miles below 

 Bagdad, and nearly oppofite to the embouchure of the Dealla 



Vol. XXXIII. 



SITTINGBOURNE, a town and parini of Kent, 40 

 miles from London, in the road to Canterbury ; contained, 

 in 1811, 230 houfes, and 1362 perfons ; 633 being males, 

 and 729 females. 



SKIDDAW, 1. 15, after fea, add— which differs little 

 from 3017 feet, the barometrical meafurement of Mr. W. 

 Allen, according to the method propofed by fir H. Engle- 

 field. (See Tranf. of the Geol. Soc. vol. iv. part 2.) 



SLATE-SPAR. See Mineralogy, Addenda. 



SLAVE, col. 2, 1. 40, for Almighty r. A mighty. 

 Col. 7, 1. 19 from bottom, for American r. African. 



Slave-Trade, Abolition of the, col. 2, 1. 12, for princi- 

 palled r. principled. 



SLIDING-RuLE. Add— Mr. Bevan has lately pub- 

 lidied in the Philofophical Magazine an ingenious modifica- 

 tion of the niding-r\de. By the inverfion of the Aider all the 

 ufual operations are performed, together with the extraftion 

 of the fquare root, and faftors of any given number are 

 found by fimple infpettion. At the fame time, the inftru- 

 ment is reduced to half its ufual fize. 



SMITH, in Geography, 1. 2, add — of whom 2201 are 

 flaves. 



SNORING. Add— See Larynx. 



SNOW, col. 2, 1. 3 from bottom, r. earth, and of bodies 

 on its furface, is prevented from efcaping by radiation to 

 the heavens during ilill or dewy nights. The caufe of this 

 additional cold does not, indeed, conftantly operate ; but its 

 prefence, during only a few hours, might efFeftually deftroy , 

 plants, which now pafs unhurt through the winter. More- 

 over, while low vegetable produfticns are prevented, by a 

 covering of fnow, from becoming colder than the atmo- 

 fphere in confequence of their own radiation, the parts of 

 trees and tall flirubs, which rife above the fnow, are little 

 affefted by cold from this caufe : for their outermoll twigs, 

 now that they are deilitute of leaves, are fo fmall, that they 

 will irery feldom become more than 2° colder than the 

 atmofphere. The larger branches too, which, if fully 

 expofed to the fl<y, would become colder than the extreme 

 parts, are, in a great degree, (heltered by them ; and, in the 

 lafl place, the trunks are (heltered both by the fmaller and 



larger parts, not to mention that the trunks muft derive 

 heat, by conduftion through the roots, from the earth kept 

 warm by the fnow. In a fimilar way is partly to be ex- 

 plained, the manner in which a layer of earth or ftraw pre- 

 ferves vegetable matters in our own fields, from the injuri- 

 ous effefts of cold in winter. It may be remarked, however, 

 that a thick covering of fnow, while it renders the furface of 

 the earth warmer than it would otherwife be, muft occafion 

 the lower atmofphere to be colder, by preventing the 

 paffage of the heat of the ground to the air, either by 

 radiation or conduftion. Wells's EfF. p. 258. See Dew 

 and Heat. 



SNOWDON, 1. 17, after fea, add — according to Mr. 

 W. Allen's barometrical meafurement, 3595,9 feet. 



SOAP-STONE. See Mineralogy, Addenda. 



SODA. See Sodium. Add — under Natron-, 1. 5, r. 

 Natron, from an erroneous fuppofition of its beino- of the 

 nature of nitre, has been by many. Col. 2, 1. 35, dele vege- 

 table alkah. Col. 4, 1. 33, for a further account of barilla, 

 fee Carbonate of Soda. Under the article Leather, 

 1. 17, for a fpecies of falt-petre r. a Carbonate of Soda; 

 which fee. 



Soda, Sodium, in Chemiflry. From the moft recent 

 and correft experiments, the weight of the atom of fodium 

 has been eftimated by Dr. Thomfon at 30, and confequently 

 the weight of the atom of foda at 40, that of oxyo-en be- 

 ing 10. 



SODAIC Powders, denote powders which are ufed as 

 a fubftitute for foda-water. ProfefTor Brande, in his courfe 

 of chemical leftures at the Royal Inftitution, took occaiion 

 to obferve, that though thefe powders produce an effer- 

 vefcence when dilTolved, arifing from the difengagement of 

 carbonic acid, the folution is very different from foda-water, 

 both in its conftituent parts and its properties. Thefe 

 powders confift of an alkaline carbonate, either of potafh or 

 foda, and a concrete acid, reduced to powder. The acid, 

 though fold as tlie citric, is in reality the tartaric acid, pro- 

 duced from the fubftance known as cream of tartar. When 

 the powders are dilfolved, the tartaric acid unites with the 

 alkali, and the carbonic acid, or fixed air, immediately efcapes, 

 occafioning a momentary eff'ervefcence. A fait is formed in 

 the folution, called by chemifts the tartrate of potalh, or 

 foda : if the former alkali has been ufed, and the acid is in 

 excefs, the fait formed is nearly infoluble, and has a harfh 

 tafte, and an irritating effeft on the ftomach. Thus, a quan- 

 tity of alkaline tartrate is taken into the fyftem, which rather 

 tends to increafe than remove obftruftions, and in many in- 

 ftances muft be highly injurious. Soda-water, if prepared in 

 the beft manner, (hould contain a very fmall portion of car- 

 bonate of foda, which has a tendency to correft acidity on 

 the ftomach ; it ftiould contain alfo about eight times its 

 own bulk of carbonic acid gas, part of which is in a ftate ■ 

 of loofe combination with the water. A confidcrable quan- 

 tity of this gas, however, appears to be united by a ftronger 

 chemical affinity, and will remain in the water fome hours 

 after it is poured out. This gas, afting as a folvent of all 

 the different eartlis, and various other fubrtances, gives to 

 the foda-water a more diluent and deobilruent efficacy, than 

 is pofieffed by common water ; and to this caufe we may 

 afcribe the good effetts of foda-water in removing bile and 

 calculary concretions. The carbonic acid, in its concentrat- 

 ed ftate, as it exifts in foda-water, is a more powerful folvent 

 of metallic fubftances than is generally fuppofed. On which 

 account the manufafture of foda-water, in vefTels of copper, 

 or other metals, ought carefully to be avoided, and too great 

 caution cannot be obferved by thofe who are in the habit of 



drinking 



