250 



KNOWLEDGE • 



[Jan. 20, 18«2. 



fncturin)^ o Booond quality of dextrin. In dry rot the taber is looso 

 and A|i(>nxy. ooatod uii the outsido with moald. Tho di«oa80 i8 

 origiiinlly iliic to Hfictoriic, and another parasilc is often present at 

 the saniti tiiiio. Wot rot, I forgot to say, (liffers from drj- rot in this 

 respect, the interior of tlie tuber is partially liquid and tho outsido 

 coated with mould. During rotting, tho potato loses half its nitre- 

 jfonous constituents and the whole of tho sngar. 



The Swectwort is formed by a paraoitc called 3/ucor mxicedo. The 

 mycelium of the parasite travels to a certain distance inside of the 

 potato, and then disappears. Bactoria rapidly destroys the plants. 

 Thers is another paru.site, called Afpfijillus niycr, which produces 

 a similar result. It seems rather uncertain as to whether cane 

 sugar or glucose is formed : some chemists say the one, others the 

 latter. 



We all are familiar with frozen potatoes, but not many of ns know 

 in what manner the frost affects them. Frost has the effect of 

 doubling the amount of sugar in the tuber, the starch diminishing 

 in proportion ; part of the protein passes from the congulable to the 

 soluble form. 



To prevent rot in potatoes, the tubers, whether sound or diseased 

 when taken from tho ground, are left in a weak solution of calcium 

 chloride — one part to a thousand of water — for half-an-hour. They 

 are then transferred to a soda solution of the same strength, after 

 ■which they are washed with clean water and uir dried. Halt kilo 

 of calcium chloride and the same amount of soda is Bufiicient for 

 250 kilos of potatoes. A kilo is a little over 2 lb. 3 oz. 



Even though potatoes axe badly diseased, they are still useful for 

 cattle food. They are best cut up and boiled or merely scalded, 

 mixed with chopped straw or cliaif, and stored in narrow trenches 

 covered up with clay. So stored, they will keep for many years. If 

 steamed, they should be kept in casks, as there is more adhering 

 moist\ire. If it is not convenient to heat them as above, they 

 should at once be sent to the distillers. 



With regard to the be.st kind of potato for yield and quality, 

 there seems to be a good deal of difference in opinion, as tlio fol- 

 lowing examples will show. 1. For quality and quantity: Cham- 

 pion, Richtnr's Imperator, Eos, &c. 2. Ilichter's Imperator for 

 yield is far the best ; is of a hardy nature, smooth, .and the stalk is 

 tall and straight. Next in order are Violet, Victoria, Irlachin, 

 Eichtcr's Snowrosc, &c. 3. For starch and yield : Eos, Aurora 

 Alcohol ; lower in yield but very high in starch, Achilles and 

 Ceree. Eichter's Imperator Early Rose, &c., very heavy yields. 

 The above forms three opinions of three chemists ; they all seem to 

 agree that the Imperator is the largest yiolder. 



I think I have now put before the readers of K.voWLKnGE tho 

 most important points in the potato which have received the atten- 

 tion of chemists during the last few years. There is one more 

 branch of the researches on which a few words may be said, and 

 that is on a few of the re.sults obtaining through jnntiuriyiy. At the 

 same time it must be mentioned that experiments on large scales 

 are still being carried out with respect to numerous manures on 

 different kinds of ground. 



The most successful way of manuring is to partially dig the 

 manure into tho ground. Tho application of nitrogenous and 

 phosphate manures without farmyard manure is much less to be 

 trusted on a poor soil than on a rich one. Manuring on fertile soil 

 is not productive of any great gain. Sheep-dung produces a yield 

 of 50 per cent, higher than any other artificial manure, and GO per 

 cent, higher than if no dung be apjdied at all. Extra supplies of 

 ommoniacal and superphosphates produce no increase. Compost has 

 the same effect as if the land were unmanurcd. except that there 

 is an increase of starch. The unmanurcd plots are highe.st in 

 disease. A good mixture is Chili saltpetre and Baker's snper- 

 phosphate in the proportion of one of the former to two of the 

 latter mixed with stable mannre. Bcme meal, one author says, 

 increases the weight of product, and it is also verj' likely that the 

 whole plant likewise increases in weight. There is another sub- 

 stance which has been tried, viz., peat, and good peat is found to 

 give even better results than good stable manure. 



If I have interested, and at the same time shown the readers of 

 K.>cowi,EDGK that there is a good deal of matter for reflection, even 

 iu the use of every-day articles of common food, such ns the 

 potato, 1 am satisfied. F. C. S. 



THE rURPLE OF THE ANCIENTS. 



FROM the interesting "Notes on the Purple of tho Ancients," by 

 Edward Schunk, Ph.D., F.R.S., the following abstract, which 

 may be interesting to the readers of KNOwr.inioE. is taken ; — 



After briefly referring to the works of Pliny and Aristotle as 

 containing accounts of the shoU-fisli used in their days for tho 

 purpose of dyeing, and also of the proces.'ses incidental to same, 

 the author proceeds to lay before the Fellows of the Chemical 



Society tho history of this intereBting dye as known to modem 

 authors and investignforB. 



A sholl-fiah from which this dye can be extracted is found on our 

 own coasts. Cole, in 1683, having discoTorod on tho coasts of 

 Somersetshire and South Wales a species of fish which, by proper 

 treatment, could be made to dye linen and silk a fine purple. 

 Reaumur, in 1710, discovered the same animal on the coast of Poitou. 



Tho shell-fish is known to conchologists by tho name of Purpura 

 capiltus. 



The results of the various observers— Cole, Bcanmnr, Dnhamel, 

 (1736), and Bancroft (1803), may be summed np aa followa : — 



1. The colour-producing secretion, which resembles pus in appear- 

 ance and consistence, is contained in a small whitish cyst or vein, 

 placed transversely under, but in immediate contact with, the shell, 

 and near the head of the animal. 



2. Tliis ims-like matter, either diluted with water or undiluted, 

 on being applied to bits of white linen or calico, and exposed to 

 sunlight, rapidly changes its colour, passing from yellow through 

 light green, deep green, and " watchct-blue," to purplish, red or 

 crimson. While these changes are in progress, a strong odour like 

 garlic or asafa-tida is given off. 



3. To produce this change of colour, the light of the sun ii 

 essential. It is effected more rapidly by the direct action of the 

 sun's rays than by that of diffused light, but it does not take place 

 in moonlight, or in artificial light. If the linen or other fabric to 

 which the secretion has been applied is kept in the dark, it remains 

 unchanged, but when exposed to the sun it becomes pmrple. even 

 after the lapse of years, though a little more slowly than at first. The 

 metamorphosis which the change of colour indicates is not sensibly 

 jiromotcd by heat. It proceeds in a vacuum and in hydrogen or 

 nitrogen gas as speedily as in air, on exposure to light. It seems 

 to be hastened by the addition of certain chemical reagents, tliongh 

 these cannot replace sunlight, which is indispensable for initiating 

 the change. 



•i. The colour produced is remarkably stable, resisting the action 

 of soaps, alkalies, and most acids ; being destroyed by nitric acid 

 and chlorine. 



Bizio, in 1855, experimented with the \furer hranduris; the con- 

 clusions deduced were similar to previous observations. A. and G. 

 do Negri, in 1875, experimented with the ilurex iranduris and 

 il. truncuhts. 



They state that the purpurogenic secretions of these two species 

 are not identical, the secretions of the former being photogenic, 

 i.e., not coloured when protected from the action of the light, 

 whilst the latter becomes violet, even in the dark, by tho sole action 

 of the air. 



Observers on the subject say that the action of light is india- 

 ponsable in the action of colouring matter in mollusca. 



The author conducts his experiments wi'.h the Purpura capillxu, 

 which he found on the rocks at low water near Hastings. He 

 worked them up immediately after collecting, as it is necessary to 

 use only live .inimals. 



Breaking the shell, he easily found the pale yellow vein at tho 

 back of the animal, which may easily be cut out for examination. 

 Putting some of the yellow viscid secretion on linen, the following 

 changes occurred : the colour changed from yellow to green, and 

 then to purple — emitting during the process the peculiar odour 

 referred to in No. 2 of the summary of previous observations. The 

 author finds that on linen, at least, the colour is not such a very 

 brilliant purple, though it seems permanent, resisting the action of 

 a strong soap liquor. 



A temperature of 100° had no effect, either in retarding or 

 hastening the formation of colouring matter. 



Besides the above, the author found that simlight was no( tho 

 only agent which would bring out the deep colour, for hydrochloric 

 acid likewise possesses this i>roperty on the veins of this remark- 

 able .shell-fish J but he thinks, at the same time, that it is open to 

 doubt whether the action in this case is similar to that produced by 

 insolation. It is interesting to watch the changes which occur in 

 colour through a microscope, and if any of the readers of Knowi.epgb 

 desire to pursue tho interesting investigation of tho properties of 

 this shell-fish, I shall be glad, at any time, to furnish them with 

 particulars of the author's observations on this point. 



Although we have, in the Old World, long since left off using the 

 shell-fish as an article for dyeing, it is still used, to some extent, in 

 America for this purpose, more especially on tho Pacific coast of 

 Nicaragua and Costa Rica. 



The following is one of the interesting accounts, given in the 

 paper, of the process as practised in Centnxl America: — 



"Some of the cotton fabrics manufactured by the Indians are 

 very durable, and woven in tasteful figures of various colours. The 

 colour most valued is tho Syrian puriile, obtained from the mn«>x 

 shell-fish, which is found on tho Pacific Coa.'Jt of Nicaragua. This 

 colour is pro.lucod of any desirable depth and tone, and is ]<erma- 



