M. TECHNOLOGY. 585 



constant stirring, in a copper kettle, with eighty to one hun- 

 dred parts of water, until a uniform mass results. Then cover 

 the kettle well, and, after cooling, pour the liquid into bot- 

 tles, which are to be well corked. Its color depends on the 

 nse of bleached or unbleached shellac. To impart the prop- 

 erty of drying quickly to oil colors for printing or painting, 

 mix an equal weight of the shellac solution with the color, 

 rubbed up thickly, using bleached shellac with light colors. 

 To prevent too rapid drying in printing, some linseed-oil var- 

 nish should be added ; but for j^ainting, oil of turpentine will 

 answer. Care must be taken to have a perfectly uniform 

 mixture with the coloring matter, and only to prepare as 

 much of it as may be needed at a time, as it will become 

 worthless by hardening, while the shellac solution can be pre- 

 served indefinitely in tightly corked bottles. By mixing the 

 varnish with yellow ochre, an excellent paint for floors may 

 be made, the brilliancy of which will be heightened by coat- 

 ing the floor, after drying, with the simple varnish. The dry- 

 ing: of other slow varnishes can be hastened bv mixino: this 

 shellac preparation with them as needed. 8 C, May 15, 1873, 

 163. 



PREVENTION OF MOULD OX GUM MUCILAGE. 



The addition of a few drops of concentrated sulphuric acid 

 to gum mucilage, and then allowing the precipitated sulphate 

 of lime to subside, will, according to Hirschberg's experience, 

 prevent formation of mould or deterioration of adhesiveness 

 for at least a year and a half; while sulphate of quinine, as 

 recommended, will not prove eflective, at least in the propor- 

 tion of one to twenty of the solution. 5 (7, 1873, x., 80. 



EXPLOSIVE OILS. 



Professor Attfield, in a lecture upon the relation of animal 

 and vegetable oils to fire, remarks that, in themselves, they 

 are much safer than mineral oils, since they do not ignite at 

 low temperatures, nor give off vapor which, when mixed with 

 a certain portion of air, explodes in contact with flame. On 

 the other hand, in their liability to spontaneous ignition, 

 when freely exposed to the air, under certain conditions, they 

 possess a dangerous property from which the mineral oils 

 are free. The animal and vegetable oils difier considerably 



B b2 



