542 



KNOWLEDGE & SCIENTIFIC NEWS. 



[September, 1906. 



algze are present in considerable numbers, and the list could 

 probably be considerably ausfmented if special attention was 

 paid to those microscopic forms occurrint; on damp walls 

 warm water tanks, etc. 



Welwifschia mirabilis. 



This remarkable plant, one of the wonders of the vesje- 

 table kin;,'dom, was discovered by Wclwitsrh in West 

 Tropical Africa. The plant has a short obconic trunk 

 mostly buried in sand; in old plants the trunk measures 

 three to four feet in diameter at the crown. The two seed 

 leaves or cotyledons are persistent, and in old plants are 

 six to nine feet lonjj ; no other leaves are produced. Quite 

 recently Professor Pearson has studied this plant in its 

 native habitat, and added considerably to our knowledee of 

 its habit and structure. The plant pfrows in desert retrions 

 and a portion of the water necessary for its ijrowth is 

 derived from the dense niRht-fopfS prevalent, but the main 

 supply is furnished by the very lon;^ root tapping; subter- 

 ranean water. When' several plants fjrow close together 

 natural grafts of a very remarkable appearance are often 

 formed. The plant is dioecious and pollination is partly, if 

 not entirely, due to insects. The maximum age attained by 

 individual'plants is probably much greater than a century. 

 Wchvifschia belongs to the ancient group of Gymnosperms, 

 and microscopic structure indicates affinity with the genera 

 Gnctum and Ephedra. The details are contained in FML 

 Trc.n. liny. Sor., 19S. 



Dry Farming. 



Under this heading Mr. Cowan indicates in the Centvry 

 Moqti-.liii' the methods by which remunerative farming can 

 be followed in regions where the rainfall is insufficient for 

 the successful cultivation of ordinary crops by the usual 

 farming methods. It has been amplv demonstrated that 

 wherever the annual average rainfall amounts to twelve 

 inches, as good crops can be raised without irrigation as 

 with it. The Campbell system of dry farming, named after 

 the pioneer " dry farmer " of arid .America, consists of a 

 scientific method of soil culture and is based on the move- 

 ments of water in the soil by capillary attraction. The 

 underlying principles are two in number, and are as follows. 

 " First, keep the surface of the land under cultivation loose 

 and finely pulverised. This forms a soil mulch that per- 

 mits the rains and melting snows to percolate readiW 

 tlirough to the compacted soil beneath, and that at the same 

 time prevents the moisture stored in the ground from being 

 brought to the surface by capillary attraction, to be absorbed 

 by the hot, dry air. The .second is to keep the subsoil finely 

 pulverised and firmly compacted, increasing its water-hold- 

 ing capacity and its capillary attraction, and placing it m 

 the best possible physical condition for the germination of 

 seed and the development of plant roots." If the method 

 indicated is thoroughly carried out a rainfall of twelve 

 inches is effectively preserved, and produces better crops 

 than in those places that have an annual rainfall of twenty- 

 four inches, and the farming is conducted on old lines. In 

 opening up a new district the land is first deeply ploutrhed, 

 behind the plough follows a special implement called a sub- 

 soil packer ; the surface is then harrowed and pulverised. 

 A year should elapse before a crop is planted, this amount 

 of time being required for the collecting and storinar of 

 water by the compact sub-soil. The surface is harrowed 

 and pulverised after each rainfall, but not at any other time. 

 When the seed is sown the land is still harrowed after each 

 rainfall until the crop is too far ad\anced to admit of this 

 process without injury. Immediately after the crop is 

 harvested the land is ploughed, followed by the sub-soil 

 packer, and harrowed after every rain until the time for 

 sowing arrives. Although the method evolved from the 

 enterprise of private individuals, the United .States Denart- 

 ment of .'\griculture has now undertaken the work of 

 demonstration in new districts, and affords facilities for 

 those interested in the matter. The development of this 

 method of farming is of i>rimary importance to the United 

 .States, where almost ex.actlv one half of the area of the 

 country has insufficient rainfall for the cultivation of crops 

 by the ordinary methods of farming. All the ordinary 

 cereals, forage plants, fruits, etc., can be grown bv the 

 method of " dry farminir." 



European Plants in the Tropics. 



It has been recorded by Lock (Ann. Itoy. Tirtf . Card. 

 Pa-adcniya) that when European plants are introduced into 

 Ceylon, the changes in habit and other respects that they 

 undergo, appear during the first year, and are permanent. 

 There is no gradual accommodation to changed environment 

 as might have been expected. 



CHEMICAL. 



By C. AiNswoRTH Mitchell, \'<.A. (Oxon.), F.I.C. 



The Absorption of Odours by Milk. 



It is well known that milk has the power of absorbing with 

 great rajiidity traces of odorous sidjstances with which 

 it may chance to come in contact. Thus milk that has been 

 exposed for some time in the cow-shed or in the shop may 

 acquire a disagreeable flavour, and even the food given to 

 the cows has not infrequently an influence upon their milk. 

 Experiments to determine the speed of the absorption have 

 recently been carried out by MM. Bordas and Toutplain, 

 who selected formaldehyde as the odorous substance, partly 

 because it can never be a noriTial constituent of milk, and 

 partly because it can be detected when only present in the 

 faintest traces. They found that milk exposed for about one 

 minute to air containing formaldehyde vapour had absorbed 

 an appreciable amount, and that even when the proportion 

 of formaldehyde in the air was only one in 100,000, aii un- 

 mistakable reaction was obtained after a few minutes' 

 exposure. .So rapid is the absorption that a reaction was 

 given by milk that had been placed in a ves.sel which had 

 contained a dilute solution of formaldehyde and had sub- 

 sequently been carefully rinsed with water. The rate of 

 absorption of the vapour appears to decrease as the milk 

 becomes older. It is suggested that this property of milk 

 might br ulili-.c(l in lesting air for traces of formaldehyde. 



The Preparation of Hydrogen from 

 Calcium Hydride. 



It h.is been shown In M. Mniss.in that when metallic 

 calciimi in a fine state nf division is heated in hydrogen it 

 absorbs a molecule of the gas, to form calcium hydride, 

 CaHo. a compound which is decomposed on contact with 

 wata- giving off hydrogen, just as acetylene is liberated 

 under similar conditions from calcium carbide. The manu- 

 facture of the hydride as a commercial product has thus 

 two stages, viz., the production of the metal calcium bv the 

 electrolysis of fused calcium chloride, and the conversion of 

 the metal into hydride by heating it in horizontal retorts 

 through which is passed a current of hvdrosren. The 

 commercial substance is in the form of irregular grev or 

 white lumps, which are very hard, and do not dissolve in 

 the ordinary solvents. They are termed liydrolUhs bv M. 

 Jaubert, who also calls attention to their value for military 

 ballooning. They contain about qo per cent, of pure calcium 

 hydride and yield about one cubic metre of hvdrosrcn per 

 kilo, on treatment with water. Thev have already been 

 used with success for the initial inflation of balloons, and 

 for the introduction of more gas without risk .and without 

 bringing the balloon to earth. 



Artificial Silk. 



.\ solution of cupric oxide in ammonia readily dissolves 

 pajier and oilier forms of cellulose, and the dissolved sub- 

 stance can then be re-])recipitated bv the addition of acids or 

 other substances. This forms the basis of several processes 

 for the manufacture of artificial silk including that embodied 

 in two recent French patents, in which the cellulose is 

 re-precipitated by means of an alkali hydroxide in the form 

 of fine threads, which are washed and freed from ammonia 

 by exposure to a current of air and tn'atment with a dilute 

 acid. It is d.aimed that the artificial silk threads thus 

 obtained arc perfectly transparent, that they have a very 

 brilliant lustre, and that they are stronger than those pro- 

 duced by other processes. The effect of the alkali upon 

 the cellulose ajipears to be similar to the ch.ange produced 

 in cotton in the so-called " mercerising " jirocess. 



