./L82i.] Scientific Intelligence, i,'73 



solution of sulphate of indigo which it is capable of discharging. From, js^mo 

 experiments made on this subject, I find that this test is not by any meaiis ,to 

 he relied upon, as will appear by the following statement; 



I prepared solutions of oxymuriate of lime and sulphate of indigo of such a 

 degree of strength that equal measures, when mixed, destroyed the colour of t^© 

 indigo. I then diluted the solution of oxymuriate of lime in the following. pro- 

 ! portions, and with the annexed results : 

 .. One measure ofsolution of oxymuriate of lime. 



One measure of water. This mixture destroyed the colour of l^th measure 

 of solution of indigo. 



One measure ofsolution of oxymuriate of lime, 



Three measures of wacer ; destroyed the colour of \.\ measure ofsolution of 

 indigo. 



One measure ofsolution of oxymuriate of lime, 



Seven measures of water. This discharged the colour of l-fg measure of solu- 

 tion of indigo. 



It appears, therefore, that by mere dilution, the discharging power of oxymu- 

 riate of lime is much increased; an equal quantity of water raising its power 

 one-fifth, three times its bulk, one-fourth; and seven times its quantity, four- 

 tenths. 



Dr. Henry, to whom I mentioned these facts, accounted for them (if I remem- 

 ber rightly) by supposing that when the concentrated solutionof oxymuriate of 

 lime is used, the sulphuric acid of the sulphate of indigo expels a portion of 

 chlorine in the state of gas, and which has no action upon the colouring matter. 

 I think it is worth the consideration of bleachers, whether some coloured solu- 

 tion could not be adopted free from this ambiguity ; for it must be evident that 

 the bleaching power of the oxymuriate is not accurately expressed by that of 

 its discharging the colour of sulphate of indigo. A standard solution of cochi- 

 neal might be made and preserved by common salt ; at least, I have no doubt 

 it may be so kept, for I find that blue vegetable infusions used as tests for acids 

 and alkalies are very perfectly preserved by it. 



IV. On the Application of Chromate of Lend, to Silk, Woollen, Linen, and 

 Cotton. By M. J. L. Las&aigne. 



The colouring matters which were formerly fixed ujaon cloths were derived 

 from organized matter; none were supplied by the mineral kingdom, although 

 so rich in colouring combinations unalterable by the air; and it is only within a 

 a few years that some of these mineral productions have been applied to the art 

 of dyeing. 



M. Raymond, of Lyons, was the first, who, by a process, equally simple and 

 ingenious, fixed prussian blue upon silk, and gave to the art of dyeing a bril- 

 liant and unchangeable colour. 



Last year, M. Braconnot, of Nancy, by applying sulphnret of arsenic (orpi- 

 ment) to cloths, procured a yellow colour, but less durable than the former. 



In the course of some experiments upon chromate of lead, I succeeded ia 

 combinmg this salt with all cloths, by a process similar to that which M. Ray- 

 mond employed to dye silk with prussiate of iron. 



After having immersed weil-cleaned skeins of silk for a quarter of an hour in 

 a weak solution of subacetate of lead, I tt)ok them out, and washed them ih a 

 large quantity of water; the object of this preparation was to combine the silk 

 with a certain quantity of subacetate of lead. These cloths, thus prepared^ 

 were afterwards immersed in a weak solution of neutral chromate of potash,* 

 they took a fine yellow colour, which continued to increase ; at the end of tea 

 minutes, the effect ceased, that is to say, the skeins of silk had received tho 

 maximum of colour, which could be yielded by the quantity of subacetate 

 v.pf, lead with which they were combined : they were then washed and dried, 



- * The solution of native chromate of iron, decomposed by nitrate of potash, and 

 •aturated with nitric acid, may be employed with equal advantage. 



