L A7o J i4U 



to a temperature of 75°* of steam in a close vessel, furnished witii a sale- 

 ty valve for half an hour,t when the cocoons were taken out, and the 

 chrysalides were found dead. The texture and color of the cocoons 

 were uninjured, but tlieir weight was reduced from six ounces to five 

 ounces three grains. J 



The following description of a furnace for steaming cocoons ia 

 France, is given by Mr. Stevenson : 



*' It is built of brick, the ground part holds the fuel, which is placed 

 upon a grate; over that, and at a little distance, a copper cauldron 

 is fixed to contain the water; above this is another grate, upon which 

 the cocoons are placed in a basket, the twigs of which are wide apart, 

 the more readily to admit the steam. To this grate and cauldron, ac- 

 cess is had by a door opening above the entrance of the fire. The fur- 

 nace is arched with bricks, that, when the door is shut^ the steam may 

 be retained within; which, in the space of eight minutes, is found effec- 

 tually to kill the insects in the cocoons. The basket is then taken out 

 and put aside, to let the cocoons dry; another basket is then placed in 

 the furnace with more cocoons, taking care to keep up the fire so as to, 

 have the water in the cauldron always boiling." 



If the furnace be arched, a safety valve should be fixed on the top; 

 a wooden cover w^ould be safer, over vdiich a woollen rug may be 

 thrown. The foundation ought to extend beyond the body of the 

 brick work, and an opening in it left to admit air to the fuel, and to take 

 out the ashes. It should be provided with a sheet iron door with 

 hinges,havinga smaller door in it, after the manner of the door of a close 

 stove; over this opening a fire stone, or cast iron plate, must be placed, 

 to support the brick work above, and to prevent it from being injured 

 when the wood is put in. A vacancy of two inches must be left be- 

 tween the boiler and the surrounding brick work, to cause the flame to 

 pass round it, before the smoke is permitted to escape. Fuel will thus 

 be saved, and the regularity of the heat be more certainly kept up, 

 which is an essential point to ensure the death of all the chrysalides. 

 That no doubt may remain on this head, the cocoons should be covcr- 

 •^d instantly, after being taken out of the furnace, with a woollen cloth, 

 one or two hours to confine the heat. They must then be dried with- 

 out delay, or the silk will be injured. Exposure to the air in dry 

 weather will effect this; in damp weather, they may be put in an oven, 

 2;ently heated, on clean cloths of linen or muslin, or in baskets. 



' The French writer from whom this account is taken, does not mention the ther- 

 mometer used on this occasion. It was citlicr that of Celsius, called the Centigrade, 

 or of Reaumur, both of which are used in France. The scale of Celsius, between the 

 freeziii"- and boihng points, is divided into 100°. The freezing point is marked 0, the 

 boilini:^ point 100° 75° of this, then, would be equal to 60° of Reaumur, or 167° of Fah- 

 renlieit. In Reaumur's scale, the space between the boiling and freezing points 'a 

 divided into 80°. The freezing point is marked 0, the boiling point 80°; on thi'* 

 scale 75° is equal to 202° of Fahrenheit, or 94° of Celsius. It is probable the wrl'T 

 refers to Ucaumur\s scale. 



* This length of time is quite unnecessary, and even injurious to the cocoor.-. 



1 Ti&;.^e c'jirt'^et do rreofranio-'e, patBorgni-, *-om. 7, p- 15, Paijs, ISCIO^ 



