130 Progress in Chemistry . (January, 



is produced in b c d. By sliding the tube, a, back and forward in the cork, b, 

 an adjustment can be given to the outlet within d, so as to secure the best 

 effect. The conditions of best effect here are identical with those in the 

 inner nozzle of the Giffard injector when it is starting its water supply from a 

 lower level, and no doubt the proportions found most efficient in that instrument 

 will prove also in this. 



According to Dr. Wiederhold, genuine Chinese lacquer-work is done over 

 tin-foil, and consists of a mixture of 2 parts of copal and 1 of shellac, melted 

 together. When fluid, there are added 2 parts of boiled linseed oil ; and, after 

 the vessel containing this mixture has been taken from the fire, there are 

 gradually added 10 parts of oil of turpentine. If colour is required, gummi- 

 gutta, dissolved in oil of turpentine, yields yellow, and dragon's blood, 

 dissolved in the same liquid, yields red. 



A plastic material of great resistance, suitable for a variety of uses, is pre- 

 pared by M. Rost, as follows : — He mixes litharge and glycerine, so that they 

 may form a creamy liquid. The mixture becomes, in a short time, a hard, 

 homogeneous mass, which readily adheres to metals, resists the action of 

 water and steam, and a temperature of 275 C. In many instances, this paste is 

 preferable to red-lead cement ; and this glycerine-litharge paste may be even 

 used, when in very fluid state, for galvano-plastic copying, since the material 

 preserves even fine engraved lines. 



Dr. Bottger prepares a glue which stands moisture without softening, by 

 dissolving in about 8 fluid ounces of strong methylated spirit £ an ounce of 

 sandarac and mastic, and next adding £ an ounce of turpentine. This solution 

 is then added to a hot, thick solution of glue to which isinglass has been added, 

 and is next filtered, while hot, through cloth or a good sieve. 



MINERALOGY. 



It must be confessed that when the discovery of diamonds in South Africa 

 was first announced in this country, some three or four years ago, there was a 

 tendency among many men of science to indulge in a little incredulity as to 

 the genuineness of the reputed discovery. But, whatever may have been the 

 doubts which were conscientiously entertained at that time, they have assuredly 

 been long since dispelled by the glowing accounts which have since reached 

 us — substantiated as those accounts have been by the arrival of larger consign- 

 ments of the veritable gems, especially by the Cape Mails during the past 

 quarter. Whilst the majority of these stones are, as might be expected, of 

 only small size, there are, nevertheless, an unusually large number of them 

 which exceed the average weight. One South-African diamond weighs 

 56 carats, and a second stone — now in the hands of Messrs. Hunt and Roskell* 

 — reaches 83 carats, while a correspondent of " The Times "f has recently 

 alluded to a fine octahedron of not less than 107 carats. Of course it is not 

 to be expected that all the stones are of fine quality, and, indeed, it appears 

 that a large proportion of the Cape diamonds are very defective. As to the 

 conditions under which the gems are found in these new districts — a subject of 

 the first importance to all who purpose adventuring forth to the diamond-fields 

 — it appears that they are commonly found, not in the beds of rivers as is 

 elsewhere generally the case, but rather on the summits or on the slopes of 

 the little kopjies or hillocks, where they are sparsely disseminated amid 

 detrital accumulations, which consist of water-worn pebbles of quartz, agate, 

 cornelian, jasper, iron-ore, itacolumite, and basalt; while in many places they 

 occur in a ferruginous gravel associated with a conglomeratic rock. We 

 understand that many practical men at the diggings believe that the distribution 

 of the diamonds bears some relation to the occurrence of certain trap rocks in 

 the district, and even suspect that in or near such rocks they may find the 

 original matrix of the gem. Without admitting for a moment that the enigma 

 of the genesis of the diamond is yet completely solved, it may be well to 



* Journ. of the Soc. of Arts, Nov. 25, 1870. 

 + Nov. ii, 1870. 



