HARJDWICKE'S SCIENCE-GOSSIP. 



171 



When separated from impurities, pulverized, and 

 the major portion of colouring matter removed, it is 

 known as " seed-lac." 



Sometimes it is melted up and made into small 

 cakes ; in this state it is known as " lump-lac." The 

 water which remains behind after the lac has been 

 softened is rich in a colouring matter akin to that of 

 cochineal, so that when strained and evaporated, a 

 beautiful purple residue is left. Cut into cakes this 

 forms another important article of commerce, viz : — 

 " lac-dye." 



Shell-lac is soluble, in anhydrous alcohol, ether, fat, 

 and volatile oils. In the alcoholic solution it forms a 

 fine varnish. 



Hydrochloric and acetic acids also dissolve it. It 

 is necessary sometimes to bleach it, for the manufac- 

 ture of colourless varnishes, sealing-wax, &c. This is 

 effected by dissolving in caustic potash, and passing 

 chlorine gas through the solution. It can then be 

 pulled and twisted into sticks. Seed-lac is much 

 more soluble in alcohol than shell-lac. Lac-dye is 

 soluble in sulphuric and hydrochloric acids. The 

 mordant for use in dyeing is generally bi-tartrate of 

 potass and protochloride of tin. 



The chief use of lac is for the manufacture of 

 varnishes and sealing-wax. The differently tinted 

 sealing-waxes are produced by adding vermilion for 

 red, ivory black for black, and verditer for blue (some- 

 times smalt is used). For a white wax, the lac is 

 simply bleached as before mentioned. 



To obtain the fine golden colour sometimes seen, 

 powdered yellow mica is incorporated with it. Shell- 

 lac is imported from Assam, Siam, and an inferior 

 quality from Bengal. 



Pegu stick-lac is exceedingly dark, and therefore 

 not fitted for the finer uses of lac ; but the finest lac 

 of a very light sherry colour comes from Circar. 



We receive something like 1,000,000 lbs. annually, 

 but a large portion of this is again exported to 

 Germany, Italy, and other foreign countries. To 

 each male insect it has been computed there are not 

 less than 5000 females, the males being twice as 

 large as the females. 



After the first melting of the lac it is usually more 

 tenacious than after subsequent meltings, which tend 

 to make it hard and brittle. The ancient Chinese 

 were well aware of this property, as is evinced in some 

 of their works of art which remain perfect to this day. 

 They are usually small boxes either in wood or metal, 

 which have had a thin coating of lac, and while soft 

 and plastic, had been moulded into various beautiful 

 forms. Some of these works of art fetch considerable 

 prices. 



At the meeting of the Geologists' Association on 

 July 3rd, Professor Blake read a paper on "The 

 Geology of the country between Bridlington and 

 Whitby, the district to be visited during the Long 

 Excursion." 



AN INTRODUCTION TO THE STUDY OF 



BRITISH DIPTERA. 



By E. Brunetti. 



{Continued frojii p. 160.] 

 (6.) Acalypterata. 



OVER five hundred species of Acalypterata are 

 British. 



An analytical table even of the groups is impossible 

 here, as Verrall admits twenty-two divisions, which 

 by his terminations would appear to be ranked by 

 him as distinct families. 



Some Continental Dipterologists make a still 

 larger number of groups. Walker divided them into 

 ten. 



Most of the Acalypterata are small flies, generally 

 obscure in colour, though some are brilliantly- 

 coloured and easily recognised, the majority, how- 

 ever, being closely allied and difficult to identify. 



A great many species have been introduced as 

 British that do not appear to be so. 



Mr. Verrall's arrangement of the genera differs from 

 that of Schiner (still probably the best Continental 

 authority), and I shall follow the former in these 

 notes. 



Coj-ciylnra, Fin., inhabits damp fields and the 

 cooler spots in woods ; long-bodied and rather short - 

 winged flies ; long 4-6 mm. 



Scatophaga, Mg., is a carnivorous genus, the 

 larv^e living in dung, two or three species being very 

 common everywhere, especially S. Stercoraria, L., 

 which in the <5 is clothed in bright yellow hair, the 

 legs also similarly clothed, the antennce and eyes are 

 black, the wings yellowish grey ; long 8-10 mm. 

 In the S (smaller) the colour is entirely grey. The 

 face is reddish in both sexes. 



Orygma, Mg., delopa, Mg., and Actora, Mg., 

 are found on seaweeds. Flies of rather an abnormal 

 appearance ; flattened ; with small heads and short 

 thick legs, often pubescent. 



In Helotnyza, Fin., the larva feeds on fungi, woods, 

 fields and pastures ; several species are British ; 

 allied. 



Dryo7Jiyza, Fin., occurs in woods ; larva lives in 

 mushrooms. Large flies ; D, analis, Fall., has 

 marked wings. 



Sciomyza, Fin., frequents short herbage and shady 

 woods. Several species are British, more or less 

 closely allied, rather small in size. 



Tetanocera, Fin., is found on aquatic plants, larva 

 aquatic ; the flies not being rare ; of good size ;. 

 stoutly-built ; usually more or less tawny in colour, 

 and from 5 to 9 mm. long. 



Limnia marginata, F., is a brownish-black fly, 

 with yellowish white face ; reddish front with two 

 black spots on inner side of eyes ; brown wings 

 covered pretty uniformly with small round grey 

 spots, the fore-border and tip being brown ;"^Iegs 

 brown ; common 



long S mm. 



I 2 



