

no 



SCIENTIFIC NEWS. 



[Aug. 3, 1 838. 



works, however, where alone such cases are likely to 

 occur, susceptible men are removed at once to some 

 other department of the works. Thus serious injury 

 from this cause is of exceedingly rare occurrence. 



Bichromate of potash is also used along with sugar of 

 lead in dyeing different shades of yellow upon cotton 

 yarns. The liquid used is cold, and the men in conse- 

 quence touch the material freely with their hands. Either 

 from this cause or from the alkaline nature of the liquid, 

 the hands are more affected than in dyeing chrome 

 blacks upon wool, and cases of impunity are much more 

 rare. 



We must, however, remember that certain compounds 

 of chromium, such as the green sesquioxide, are abso- 

 lutely harmless to prepare and to use. The reason of 

 this is that they are absolutely insoluble, and cannot be 

 volatilized. This is a fortunate circumstance, since the 

 chrome greens (Guignet's green) can be used with 

 safety instead of the arsenical greens in the manufacture 

 of wall-papers. 



This naturally brings us to arsenic, generally regarded 

 as the most formidable of the mineral poisons. The 

 fact that it is colourless and tasteless, and therefore may 

 find its way unsuspected into articles of food and drink, 

 ought to lead to the abolition of its use wherever there 

 is no absolute necessity. Thus we can see no justifica- 

 tion for the employment of arsenical preparations in the 

 manufacture of paper-hangings. Still worse is the case 

 when tarlatans are got up with green arsenical colours, 

 Paris green, Scheele's green, etc., mixed up with starch 

 and not firmly fixed upon the fibre. The air of a ball- 

 room where such tarlatans are worn must contain a 

 certain proportion of arsenical dust. 



Now it will be generally admitted that if the wearers 

 of such arsenical tissues and the inmates of rooms hung 

 with arsenical papers are in danger of being attacked, 

 the workmen employed in making such colours or in 

 applying them to the paper and the cloth will scarcely 

 escape with impunity. Now is this, in fact, the case ? 

 According to Dr. Jabez Hogg, who has made a special 

 study of the action of arsenical pigments, " workmen 

 while engaged in stripping off old wall-papers from 

 rooms preparatory to re-papering are frequently obliged 

 to leave their work from attacks of diarrhoea and other 

 stomach derangements." 



But what must we say of the manufacture, and conse- 

 quent use, of arsenical pigments where the poison plays 

 no demonstrable part at all in the production of the 

 colour desired ? Yet reds, blues, greys, and browns 

 have, on analysis, been found to contain arsenic. 

 Whether this arises from some unscientific method of 

 manufacture or from the careless use of impure materials 

 it is not our place to pronounce. 



Arsenic was in -former days very generally found in 

 aniline colours. The reason was that magenta was at 

 that time chiefly manufactured by the arsenical process 

 (Medlock's patent), and as a variety of other colours 

 were obtained from its transformations, the aniline 

 colours came to be regarded as, generally speaking, 

 poisonous. To a very great extent this process is now 

 abandoned, and where it is still used the product is 

 purified with such care that arsenic is not to be expected 

 in the aniline dyes sold by the more eminent makers. 



Arsenic is used to a considerable extent by calico- 

 printers in the so-called " dung-substitutes." In those 

 styles where a piece of calico is dyed after it has been 

 printed with various mordants it has to undergo a 



cleansing process, called in France degommage, and in 

 England dunging, because it was performed with the 

 dung of cows suspended in water. To supersede this 

 unpleasant substance, certain preparations were de- 

 vised, under the name of dung-substitutes, and were 

 composed chiefly of arseniates of soda. Probably none 

 of this arsenic would remain on the tissue to the injury 

 of the future wearer ; but the spent liquors and the 

 rinsing waters would convey a certain quantity of 

 arsenic down into the sewers and the rivers, and if not 

 precipitated in an insoluble form would be exceedingly 

 apt to turn up where it was by no means wanted. We 

 forgot to mention that the waste waters from chrome- 

 black and chrome-yellow dyeing also find their way into 

 the streams. 



A great channel for the promiscuous distribution of 

 arsenic is the manufacture of sulphuric acid, which is 

 to the chemist what iron is to the engineer — in use 

 always and everywhere. Now, by far the largest quan- 

 tity of the sulphuric acid of commerce is obtained from 

 iron-pyrites (sulphuret of iron), a mineral which most 

 unfortunately is rarely, very rarely, absolutely free from 

 arsenic. Hence the poison finds unsuspected access into 

 a vast variety of products. A cheap and practicable 

 method of producing sulphuric acid free from arsenic is 

 one of the prizes for which chemists are earnestly striving. 

 (To be concluded.) 



WORK FOR NATURALISTS' CLUBS. 



III. — The Structure of a Feather. 



IT is not easy to find a better subject for an evening's 

 demonstration than a feather. The following 

 materials should be collected : — a few quills, some bodj'- 

 feathers of a fowl, pheasant, or partridge, a peacock's 

 plume, and a fresh pigeon or other bird, unplucked of 

 course. If a lantern can be had, it will be useful to put 

 up between glass plates a piece of the peacock's feather, 

 a double-shafted body-feather of one of the gallinaceous 

 birds named above, an emeu's feather, and also some 

 photographic copies of good drawings. Plate i of 

 Nitzsch's Pterylography (Ray Society) is recommended, 

 but various illustrated text -books may be drawn upon for 

 figures of the simpler points. An effective model of the 

 shaft, barbs, and barbules may be made of pieces of card 

 cut to the proper shape, and fitted by means of saw-cuts 

 into wooden bars. 



Observe first the primary divisions of a feather, viz., 

 the quill, shaft, and vane. The shaft is occupied by a 

 dense pith ; the quill is empty, except for some light and 

 dried-up capsules, which form a chain within it, and 

 which represent the shrivelled remains of the formative 

 follicle. At the bottom of the vane, and on the inside of the 

 feather, will be seen a scar, the umbilicus. Down to this 

 point the originally cylindrical feather has split along one 

 side ; below, the tube remains complete. Show by 

 means of a paper model that if a closed cylinder be split 

 open in its upper half, while it remains entire below, f 

 passage into the inside of the tube must exist where the 

 closed and open parts meet. In immature feathers the 

 apex of the formative papilla can often be seen to project 

 from the umbilicus (see figure). 



The structure of the barbs which compose the vane 

 may next be considered. Each is a knife-blade, having 

 its thick edge turned outwards, i.e., away from the bodj 

 of the bird. The barb carries a double row of barbules. 



