IV. 
INTRODUCTION. 
37 
is repeatedly digested with hot water, when it yields a mucilage of a brownish red 
colour and of a sweetish but very disagreeable taste. When evaporated to dryness, 
this mucilage leaves a saline semicrystaline mass. This being repeatedly treated 
with boiling alcohol, yields the mannite in “ large hard prisms of a fine silky 
lustre.” Halidrys siliquosa , Laminaria digit at a, Fucus serratus, Alaria esculent a, 
PJiody menia palmata , &c. are stated by Dr. Stenhouse, from whose memoir this 
account is condensed, to contain from 1 to 5 or 6 per cent, of mannite. 
In summing up the economic uses to which Alga? have been applied, I must not 
omit to mention their application in the arts. The most valuable species, in this 
point of view, with which we are acquainted, is the Gracilaria tenax of China, 
under which name probably more than one species may be confounded. Of this 
plant, on the authority of Mr. Turner, (Hist. Fuc. vol. 2, p. 142,) “the quantity 
annually imported at Canton is about 27,000 lbs., and it is sold in that city at about 
6d. or 8d. per lb. In preparing it, nothing more is done than simply drying it in 
the sun ; after which it may be preserved, like other Fuci, for any length of time, 
and improves by age, when not exceeding four or five years, if strongly compressed 
and kept moist. The Chinese, when they have occasion to use it, merely wash off 
the saline particles and other impurities, and then steep it in warm water, in which, 
in a short time, it entirely dissolves, stiffening as it cools into a perfect gelatine, 
which, like glue, again liquefies on exposure to heat, and makes an extremely pow- 
erful cement. It is employed among them for all those purposes to which gum or 
glue is here deemed applicable, but chiefly in the manufacture of lanthorns, to 
strengthen or varnish the paper, and sometimes to thicken or give a gloss to gauze 
or silks.” Mr. Turner derived the above information respecting G. tenax from Sir 
Joseph Banks ; but recent travellers tell us that Gracilaria spinosa , known colloqui- 
ally as Agal-cigal * yields the strongest cement used by the Chinese, and that it is 
brought in large quantities from Sincapore and neighbouring shores to the China 
markets. Probably both species are esteemed for similar qualities. 
Several Algje are used in the arts in a minor way. Thus, according to Dr. 
Patrick Neill, knife-handles are made in Scotland of the stems of Laminaria digi- 
tata. “ A pretty thick stem is selected, and cut into pieces about four inches long. 
Into these, when fresh, are stuck blades of knives, such as gardeners use for pruning 
or grafting. As the stem dries, it contracts and hardens, closely and firmly em- 
bracing the hilt of the blade. In the course of some months the handles become 
quite firm, and very hard and shrivelled, so that when tipped with metal they are 
hardly to be distinguished from hartshorn.” 
On the authority of Lightfoot,f the stems of Chorda filum , which often attain the 
length of thirty or forty feet, and which are popularlv known in Scotland as “Lucky 
Minny’s lines,” “ skinned, when half dry, and twisted, acquire so considerable a 
degree of strength and toughness,” that the Highlanders sometimes use them as 
fishing lines. The slender stems of Nereocystis are similarly used by the fishermen 
in Russian America. In parts of England bunches of Fucus vesiculosus or F. 
See, tile Voyage of H.M.S. Scimarang. 
f FI. Scot. vol. 2, p. 964. 
