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wet sponge, he observed, that the oystershell powder was taken at randoin, and added to the cheese till it had acquired the consistency of a paste capable of being spread on paper.

The committee having obtained from Mr. Bachelier a few leaves of paper covered with thin paste, found from the very deep black immediately given it by the hidrosulphuret of potash, that it contained a considerable quantity of oxide of lead, the presence of which there was no reason to suspect in the preservative stucco, so that they could not be considered as the same.

It remained therefore to analyse the stucco, which was done by Mr. Vauquelin; though, as a very small quantity only could be obtained by scraping the pillars, it did not admit of repeated trials. The results of his analysis gave

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No animal

tables emitted.

Organic matter, an indeterminate quantity

102.73

The surplus of 2.73 Mr. Vauquelin ascribes either to the matter not having been dried to the same degree, or to the escape of a little carbonic acid during the calcination.

The presence of animal matter was sought for, but not particle could be separated. The smell it emitted during but the pungent smell of calcination no way resembled that of aminal matters; on burning vege; the contrary it had the pungent sharpness of vegetable substances. On being exposed to the action of heat in a retort however, a clear and almost colourless liquid came over, from which potash expelled a very evident ammonical Indications of vapour. This indicates, that some animal substance entered into the composition, but that in time it was decomposed, and left only an ammonical salt. The brownish colour it acquired in the fire also proves, that some animal · matter still remained in it; though altered in its nature, since it neither emitted the smell proper to such substances, nor yielded any preceptable quantity of oil. Lastly,

animal mat

ter.

Lastly, this matter yielded no appreciable quantity of No alumine. alumine, so that it may be presumed no alum was employed

in the composition.

Mr. Bachelier having some of the paper that had been Analysis of the prepared by his father, the coating of this was analysed, and paper coating. the result indicated, that

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Calcined gypsum...

Ceruse or carbonate of lead...

had entered into its composition.

56.66

23.34

20

On these proportions more dependance can be placed This more than on the former, since it was impossible to detach the be depended plaster from the pillars without some of the substance of the

stone itself,

on.

That the caseous part of the milk is the proper vehicle for Cheesy matter the powders we learn from the positive testimony of Mr. Ba- the vehicle. chelier, the son; and its utility is confirmed by the experiments of Mr. d'Arcet published some years ago*.

compound unquestionable.

Of the efficacy of Mr. Bachelier's composition there can Efficacy of the be no doubt, as we have irrefragable and still existing testimony of it; nor would it be difficult to estimate this beforehand, when we consider the causes, that produce the gradual decay of the finest buildings in this capital, and the means of guarding against them.

ble to this al

Hard and fine grained calcareous stone, susceptible of a Stone not liagreater or less degree of polish, is not liable to this altera- teration, tion. It is therefore owing to the nature of the stone commonly employed, which is of a loose and unequal texture, and liable to it. 'filled with cavities, and found by analysis to contain 10 or 12 per cent of silex, and frequently 3 or 4 of oxide of iron. The difference of the stones from the quarries near Paris is evident from the tables of Mr. Rondelet, in his Treatise on the Art of Building; where we see, for example, that what is called the grignard of Passy is of the specific gravity of 2.462, and supports a weight of 6750 kil,; while the lambourde of St Germain has only 1.560 sp. grav., and is

Déc. phil. an X, No. 5. The pamphlet entitled l'Art de peindre au Fromage, ou en Ramekin, which Mr. d'Arcet regrets his being unable to procure, was foreign to the subject, as it related to painting with soap of wax. [See Journal, Vol. 1, p. 212.]

crushed

these stones.

crushed by a weight of 921 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 Linnaeus senoculata, the cellar spider of Geoffroy, should find on the surface of this stone a convenient situation to shelter itself, deposit its eggs, and spread the nets in which it awaits its prey. Its web extends circularly round the cavity, 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 sixtyeight 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 preventing this.

Other means.

If it be asked, how is this to be prevented? the answer is easy. By a composition that resists water, will adhere to the stone so as not to scale off, has a sufficient degree of consistency 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 assemblage of coarse grains the smooth surface of polishable stones, in which it appears these insects cannot nestle. And this we think may be expected from Mr. Bachelier's stucco.

Meantime I must observe, that, in the present state of our chemical knowledge, other means of fulfilling these conditions 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 he has found the same habits in Lis. ter's aranea atrox.

their acid, to give it a sort of covering, that would render it as unalterable as the stone of Logozan in Estrainadura. It is equally known, that sulphate of barytes resists all agents in the humid way; and we might certainly coat the stone with this earthy salt, by first impregnating it with a solution of sulphate of iron, zinc, magnesia, alumine, &c., and immediately washing it over with barytes water *. The insolubility of oxalates and tartrates of lime, and the adhesion they contract by deposition even on polished substances, suggest processes for washes not less solid; as the acids added to these salts to render them temporarily soluble, saturating themselves with their base from the substance of the stone itself, would not fail to connect together all the grains, fill up their intervals, and completely close the pores. Trials made with a view to ascertain the justice of this reasoning have confirmed the expectation of a successful result; since on the most porous stones they have produced a surface, on which the eye could see no appearance of coating, but which, being rubbed with wet black cloth till the cloth showed signs of wear, was not in the least soiled by it.

Preparations of this kind however would be much more The latter too expensive than Bachelier's stucco, so that their use must be expensive. restricted to the preservation of sculpture of extreme deli

cacy.

For farther satisfaction trials have been made with diffe- General rerent kinds of stone, and stucco made in imitation of Bache- sults of expe lier's. These have given rise to the following observations.

1. All the compositions in which alum water was employed soiled the fingers, and were washed off by water.

2. The cheese that acquires the greatest consistency with dry substances is that which is almost entirely deprived of the butyraceous and wheyey parts. Mr. d'Arcet, in the paper already quoted, had remarked, that these were more detrimental than useful, that painting with milk would not resist water, and that the cheese called fromage à la pie might

riments.

Accident furnished Mr. d'Arcet with a striking proof of the readi- Filtering stone ness with which this change of bases by superior affinity will fill the pores spoiled by ac cident. of the most porous stones. A capsule full of strontian water happening to be overturned into a filtering stone, it never after let through a single drop of water,

be

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Proportion of cheese.

Preparation of

be used after it had grown dry, though less advantageously than when fresh made and well drained.

3. A mixture of this cheese with lime simply forms a paste, that adheres but slightly even to coarse grained stone, and not at all to paper.

4. Calcined gypsum, which in a small dose facilitates the union of the lime and cheese, renders the paste hard and clotty, if it be used in too large proportion.

5. It had appeared, that whiting, which is used in paper hangings, might be admitted into the preparation: but it was found, that, if this earthy substance, which in a process described by Mr. d'Arcet is carried to twenty times the weight of the lime, may be used with success for inside work, it would make too thick a coat, and would not adhere so strongly to the stone.

6. The addition of a very little ochre, or red oxide of iron, to this preparation, will give it such a tint as may be wished, without altering its properties.

The proportion of cheese must depend in some measure on the state in which it is, and cannot be determined precisely but by the condition of making a soft paste. A fourth of the weight of the solid matters appears to be a sufficient quantity of cheese fresh from the press.

The quantity of lime to be used at once being deterthe compound. mined on, it is to be slaked in as little water as possible, but enough to make it pass through a sieve not very fine, in order to separate the parts that will not slake. This is to be triturated with the cheese to the consistence of a soft, smooth, and coherent paste. To this are to be added the calcined gypsum and the white lead, which must not be adulterated with chalk, and by farther grinding on the stone with a little water the whole is to be reduced to a pap, rather thick than fluid. Lastly it is to be diluted with common water the moment of using it, which is to be done with a painter's or varnisher's brush.

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