SWAGES 965 



some vegetable colours, as well as the gas itself, viz. those of roses and violets, &c., 

 but in most cases the colours may be restored by treating with a weak acid or alkali. 

 It cannot be respired in the pure state, as it immediately causes spasm of the glottis ; 

 but if diluted with air and then breathed, it acts as a local irritant, exciting cough, 

 pain, and a sense of dryness of the mouth and throat. Its sp. gr. is 2-2 ; 100 cubic 

 inches weighing 68'69 grains. Its solution in water may be kept any time without 

 change, as long as air is excluded, but when air gains access to it, it is gradually con- 

 verted into sulphuric acid. 



SUIiPHURS. Impressions taken by the goldsmiths of the sixteenth century from 

 the engravings executed on plate, paxes, &c., and which they obtained by spreading 

 a layer of melted sulphur on the face of the plate, producing a cast in relief of the 

 lines engraved. Some few of these proofs exist in the British and Continental 

 Museums, and are known as sulphurs. They are amongst the rarest specimens con- 

 nected with the art of engraving. 



STJIiPHYDROlVIETRTr. The determination of sulphur. 



SUMACH, or SHT7ZVXACH. A species of the genus Ehus, used in tanning. It 

 is known also as sumac and shumac. It consists of the ground-leaves, foot-stalks, 

 and young twigs of several varieties of plants, technically known as sumacs, but 

 botanically belonging to the genus Rhus of the Natural Order Anacardiacecs. The 

 sumac of commerce is chiefly obtained from the Rhus Coriaria, in the following 

 manner: A short time before the blooming of the plant in June or July, the 

 younger twigs are cut off, dried in the sun, next beaten, so as to detach the leaves and 

 flower panicles, which are next coarsely ground up by means of millstones. The 

 shrub just named is a native of Asia, but is cultivated in many parts of Europe, more 

 especially in Sicily, Spain, Southern France, and Hungary. Sumac is also prepared 

 from the Rhus Cotinus. 



In the South of France a peculiar kind of sumac is prepared, and known locally as 

 redout or redou. It is derived from the Coriaria myrtifolia, or tanner's-herb, which 

 contains a violently poisonous substance. 



The leaves of the Arbutus TJva-ursi, better known in pharmacy than in technology, 

 are used as sumac in Dalecarlia, Sweden. 



The following are the chief varieties of sumac known in the trade : 



Sicilian Sumac. The most esteemed article, fetching always a high price, 



Spanish Sumacs. Exported from Malaga, Priego or Mohua, Valladolid. 



Portuguese Sumacs. From Oporto. 



Italian Sumacs. 



French Sumacs. 



The articles are classified here according to their amount of tannin. 



Imports in 1873. 



Value 

 Tons 



From Italy 11,806 183,037 



Austrian Territories . . . . 1,304 16,017 



Other countries .... 672 9,327 



Total .... 13,782 208,381 



SU3MFX.OWER Oil.. See OILS. 



sumr consists of the fibre of the Crotolaria juncea, a totally different plant from 

 the Cannabis sativa, from which hemp is obtained. Sunn is grown in various places 

 of Hindostan. The strongest, whitest, and most durable species is produced at 

 Comercolly. It is also known as Bengal Hemp. 



SUNSTONE. A variety of felspar, of a pale yellowish colour, found in Siberia. 

 It is almost perfectly transparent when viewed in one direction; but by reflected 

 light it appears full of minute golden spangles. See FELSPAR. 



SUPERPHOSPHATE, properly superphosphate of lime, much used as a manure. 

 See PHOSPHATES, and MANURE. 



SUSSEX MARBXiE. Thin bands of shelly limestone, occurring here and there 

 in the Weald Clay, especially in the upper part. This limestone is principally com- 

 posed of the remains of freshwater snails, a species of Paludina, and it has been 

 named Sussex marble, in consequence of its great development in that county. 

 Although the stone is not remarkable for any particular beaiity of colour, being 

 generally of a uniform bluish or greyish-green tint, the sections of the chambers of 

 the shells give it, when polished, a pleasing appearance, and it has, in consequence, 

 been frequently made use of in former times in the construction of tombs and sepulchral 

 monuments in many of our older churches. H. W. B. 



SWAGES. Tools employed in shaping metals. 



