184 ON THE DEFECTS AND WANT OF STRENGTH 



than the appreciation of the fraud itself, for Pliny tells us that, in hi* 

 time, the papyrus, moistened with the muddy water of the Nile, which 

 held in suspension a very fine clay, was frequently spongy and sucked 

 up the ink, by reason of too large an intermixture of this mud ; so much 

 knavery is there, added he (tantum in estfraudis !). 



Nevertheless, used in moderation, kaolin is not so destructive as 

 might be supposed. When a strong substance i3 mixed with the pulp, 

 and the whole carefully beaten, it has the advantage of making the 

 paper pure and even, by "causing the pores to disappear, which the fibres 

 of the cellulose form in the sheet. The kaolin, which is now made use 

 of by almost all paper-makers, under the specious pretext of giving 

 more colour to the paper, 'but also undoubtedly with the object of aug- 

 menting the weight of their manufacture, gives to the paper, when it is 

 used in too large a proportion, a dull appearance. The sheet is then 

 soft, weak, and without consistency, especially when soft rags are in 

 excess, and the stuff is short. Moreover, by the scratching of pens, 

 particularly those of steel, the interposed aluminous earth is detached 

 from the paper, which very quickly soils and roughens ; for this reason 

 care is taken to introduce, relatively, a much less quantity of kaolin into 

 writing paper than into printings. 



It is also sought by the addition of a large quantity of starch, to 

 correct the want of strength in paper, arising from the introduction of 

 these pulverulent substances, just as, by glazing, it is sought to modify 

 the downy appearance which the presence of cotton gives to paper. 



It is only in an exceptional manner that certain makers have 

 recourse to sulphate of lime (plaster or gypsum), mentioned by Baron 

 Dumas, as being largely consumed for this object. Plaster is far from 

 lending itself equally well to this application as the pure silicate 

 of alumina, which, by reason of its fine grain, unctuousness, and 

 plastic properties, combined with its cheapness, is almost exclusively 

 employed at the present time. If the makers do not employ in preference 

 baryta, and the sulphate, or carbonate of lead, which, equally white as 

 kaolin, have the advantage of being heavier, and consequently should 

 be preferred to effect the proposed object, it is because these substances 

 are dearer than China clay, and, moreover, the salts of lead would 

 have the inconvenience of turning yellow, by contact with the 

 vapours of sulphuretted hydrogen. Be.sides, the heavy specific weight 

 of these substances causing them to sink to the bottom of the engine, 

 the pulp would not be so homogeneous as kaolin, which remains sus- 

 pended in the semi-liquid mass of the stuff. It has, however, been 

 found possible to obtain plaster and sulphate of baryta in the required 

 state of tenuity, and free from clots, by precipitating them from solu- 

 tions of chloride of calcium, or of barium, by means of sulphuric acid 

 or of sulphate of alumina, introduced into the pulp itself. The mix- 

 ture of zinc white would, perhaps, be a further improvement in this 

 practice, which can be considered as lawful, since it is tolerated, without 



