68 REPORT-'— 1855. 



On the Marine Aerated Freshwater Apparatus. By Dr. Normandy ' 



On a simple Volumetric Process for the Valuation of Cochineal. By Dr. F. 

 Penny, F.R.S.E,, Prof, of Chemistry, A7idersonian University, Glasgoiv. 



Within the last few years several eminent chemists have rendered important ser- 

 vice to the arts by devising simple and expeditious processes for estimating the value 

 of technical products. In the application of volumetric methods of analysis their 

 labours have been most successful. 



The great aim has been to combine economy of time with simplicity of manipula- 

 tion and accuracy of result. The variety and extent of these investigations may be 

 sufficiently indicated by referring to the processes of clilorimetry, to Bunsen's beautiful 

 method for iodine, Marguerite's process for iron, Liebig's process for chlorine and 

 urea, Pelouze and Schwarz's processes for copper, the assaying of silver according to 

 Gay-Lussac, the employment of bichromate of potash for the estimation of iron, tin, 

 iodides, &c., and the recent methods of testing the pntash-prussiates. 



In this field of inquiry, however, much still remains to be done, both as regards 

 the improvement of the methods already in use, and the extension of our powers by 

 the application of new processes. The discovery of trustworthy methods of deter- 

 mining the economic value of madder, cocliineal, oak-bark, logwood, and of many 

 other articles, is a boon still to be desired, and the attainment of which is confidently 

 expected from the progress of technical chemistry. 



Several processes have been proposed for testing cochineal. The high price and 

 variable quality of this article, as well as its liability to accidental impurity and occa- 

 sional adulteration, render the discovery of a suitable method exceedingly desirable. 



The adulterations of cochineal have frequently been noticed. The use of sulphate 

 of baryta and bone-black was detected and exposed many years ago. It has also 

 been adulterated with powdered talc and carbonate of lead, and it has at times been 

 found mixed with a coloured paste, moulded into small grains, to resemble, as closely 

 as possible, the form and outline of the insect itself. 



Ground cochineal is occasionally adulterated with spent or exhausted cochineal ; 

 and Persoz states that the entire insect, exhausted more or less with water acidulated 

 with vinegar, has been dried and sold, or mixed with sound cochineal. 



The substance called ' Garblings,' the refuse from riddling or sifting cochineal, has 

 likewise been added to the article in bulk. 



As imported, the principal impurities are sand, fibrous organic matter, and a 

 resinous substance resembling seed-lac. 



Of the different methods that have been suggested for ascertaining the tinctorial 

 powers of cochineal, the simplest consists in exhausting a known weight with water, 

 and examining the liquor, made up to a certain volume by the addition of water, in the 

 colorimeter, according to the method proposed by Labillardiere for madder and indigo. 



Berthollet estimates the comparative richness of cochineal in colouring matter by 

 dosing a known quantity, dissolved in water, with a standard solution of chlorine. 



An ammoniacal solution of alum has also been proposed for the volumetric valua- 

 tion of cochineal. The insect in fine powder is exhausted with water, and the liquor 

 and washings, being concentrated by evaporation, are treated with a standard solution 

 of alum, until the whole of the colouring matter is precipitated. From the propor- 

 tion of alum liquor used the comparative quality of the cochineal is easily determined. 



Brokers and others estimate the value of cochineal by boiling a few grains of the 

 sample t with a slip of flannel for a quarter of an hour, in water to which small 

 quantities of cream of tartar and chloride of tin are added. The flannel is afterwards 

 washed and dried, and according to the shade and intensity of the scarlet colour 

 communicated, the value of the cochineal is judged of. 



The process now proposed, though far from fulfilling all that could be wished, has 

 been found extremely useful in comparing different samples of cochineal, and has 

 proved equally serviceable in examining specimens of lac-dye, than which few com- 

 mercial substances are more variable in quality. 



It is based on the well-known bleaching properties of red prussiate of potash in 



* This invention is patented, and is employed in the Navy and at Heligoland, 

 t Normandy, Commercial Analysis. 



