24, STUCCO FOR PRESEUTINQ STONE. 



crushed by a weight of 9'21 kil. The prices of these two 



kinds of stone differ too in the proportion of 26 to 10. 



Spiders form It is not at all strange, that the little spider called by 



their webs on Linnteus senoculata, the cellar spider of GeofFroy*, shoijd 

 these stones. r\.i- .. 



find on the surface of this stone a convenient situation to 



shelter itself, deposit its eggs, and spread the nets in which 

 it av/aits its prey. Its web extends circularly round the ca- 

 vity, that serves as its den, forming round spots of 3 or 4 

 cent, [1 in. or 1|] radius. It is not thirty years since the hotel 

 des monnoies was built, and I have counted no less than sixty- 

 eight of these dark gray spots on one of the pillars of the 

 vestibule. Similar ones are found not only on the stone, 

 but on the coatings of plaster, and on the walls covered with 

 common stucco. It is particularly in the joints and angles, 

 that the insect begins to fix itself. I have seen several on 

 walls, the stucco of which had been coated afresh within less 

 than seven years. These spots at length form a continued 

 coat, retaining the sloughs of these insects, the remains of 

 those on which they feed, and the dust raised by the wind> 

 so that lichens soon take root in them. 

 Mode of pre- If it be asked, how is this to be prevented ? the answer is 

 venting this, ^^gy^ gy ^ composition that resists water, will adhere to 

 the stone so as not to scale off, has a sufficient degree of con- 

 sistency to stop the pores accurately, is liquid enough to be 

 spread as a wash, and uniformly to ice over, as it were, all 

 the saliant and indented parts, without thickening the angles 

 or blunting the edges, and lastly which gives to the assem- 

 blage of coarse grains the smooth surface of polishable 

 stones, in which it appears these insects cannot nestle. An4 

 this we think may be expected from Mr. Bachelier's stucco^ 

 Other means. Meantime I must observe, that, in the present state of 

 our chemical knowledge, other means of fulfilling these con» 

 'ditions may be pointed out. We know for instance, that 

 phosphate of lime is one of the most fixed combinations: it 

 would be sufficient therefore, to wash over the stone with 

 phosphoric acid more or less diluted, or with phosphate of 

 lime, lead, magnesia, &c., held in solution by an excess of 



* Mr. Latreille informs me, that hfe his found the same habits in Lis- 

 ter's arcnea atrox. 



their 



