August i6, 1889.] 



SCIENCE. 



109 



basket. The essence is so valuable, that the operatives are closely 

 watched. Six men can work up 8,000 lemons a day : two cut off 

 the peel, while four extract the essence, and obtain 136 gallons of 

 lemon-juice and 7 pounds of essence. In the extraction of essence, 

 defective fruit — thorn-picked fruit, blown down by the wind or 

 attacked by rust — is used. This fruit is sold by the "thousand," 

 equivalent to 119 kilograms, and thus classified: (i) mixed lemons 

 as they come from the groves during December and January, of 

 good quality but not always marketable, often from top branches ; 

 (2) lemons from March blooms ; (3) lemons refused at the pack- 

 ing-houses ; (4) dropped fruit ; and (5) shrivelled or deformed 

 fruit. 



Lemons grown on clay soil yield more essence and juice than 

 those grown on sandy or rocky soil. Dealers sometimes adulterate 

 their essences with fixed oils, alcohol, or turpentine. Adulteration 

 by fixed oils is detected by pouring a few drops of essence on a 

 sheet of paper, and heating it : upon the evaporation of the essence, 

 a greasy spot will remain. Alcohol is detected by pouring a few 

 drops of the essence into a glass tube in which a small quantity of 

 chloride of lime has been dissolved. The tube is then heated and 

 well shaken, and, its contents being allowed to settle, the essence 

 will float on the denser liquid. For the production of raw and 

 concentrated lemon-juice, the following is the system employed. 

 When the lemons have been peeled and cut in two, as described 

 above, they are carried to the press and thrown into large wicker 

 bags, circular in form, and then well pressed. If the juice is to be 

 exported raw, only perfectly sound lemons can be used ; but if the 

 juice is to be boiled down, one-fifth of the lemons may be of an 

 inferior quality. The juice from sound lemons is yellowish in 

 color, and has a pleasant aroma : its density decreases with age. 



With all classes of lemons the yield of juice and its acidity vary 

 considerably from month to month. The amount of juice increases 

 from October to April, its acidity and density decrease ; and the 

 same is the case with the density of the essence, owing to winter 

 rains. An addition of five per cent of alcohol will prevent raw 

 lemon-juice from spoiling. Lemon-juice is adulterated with salt 

 or tartaric acid. Raw and concentrated lemon-juice is exported in 

 casks of 130 gallons capacity. It requires about 1,500 lemons to 

 yield 26 gallons of juice, while it takes 2,500 to yield the same 

 quantity of concentrated juice, and 2,000,000, more or less, accord- 

 ing to their acidity, to give a cask. Experience has shown that 

 the lemons of the province of Messina, especially from the eastern 

 shore, contain more acidity than the lemons grown elsewhere in 

 Sicily. The value of lemon-juice is governed by its acidity. The 

 rule is that concentrated lemon-juice shall show 60 degrees of 

 acidity (the juice extracted from the bergamot or the sour orange 

 must show 48 degrees, or one-fifth less than that derived from the 

 lemon ; it also sells for one-tifth less than lemon-juice). Formerly 

 a citrometer, known as Rouchetti's gauge, was used to ascertain 

 the percentage of acidity ; now, however, resort is had to chemical 

 analysis, which is said to be more satisfactory to both buyer and sell- 

 er. Of late years a new article, known as vacuum pan concentrated 

 natural juice of the lemon, has been manufactured at Messina. 

 The juice concentrated by this method contains 600 grains of 

 crystallizable citric acid for every quart. It is exported in casks 

 containing 112 gallons, and in half and quarter casks. It is also 

 shipped in bottles of 500, 300, and 150 grains each. Consul Jones 

 says, in conclusion, that there is an establishment at Messina, prob- 

 ably the only one of its kind in Italy, in which crystallized citric 

 acid is prepared. It takes from 340 to 3S0 lemons to make a 

 pound of citric acid, which sells at about forty-four cents. The 

 quantity of essence of lemon exported from Messina during the 

 year 1887 amounted to 440,000 pounds avoirdupois, valued at 

 $625,000 ; while of lemon-juice, 4,438 pipes were exported during 

 the twelve months ended Nov. 30, 1887. 



ARTIFICIAL SILK. 



Science and industry are ever combining to copy Nature, and 

 even dare to attempt improvements on her processes. The Champ 

 de Mars contains many illustrations of this ; but perhaps the bold- 

 est and most curious attempt of this kind is to be seen in the manu- 

 facture of artificial silk, described in a recent number of Engineer- 



ing. Near the end of the Machinery Hall, that end by the Avenue 

 du Suffren, and quite close to the elevator which raises passengers 

 to the travelling bridges, there is an exhibit showing the manufac- 

 ture of silk without any aid from silkworms, and on a system which 

 appears to be entirely novel, and is certainly of wonderful sim- 

 plicity. The silk industry has seen great vicissitudes, and has had 

 to suffer many cruel troubles from disease both of the worms and 

 of the trees they feed upon ; but up to the present we believe that 

 it has been spared the struggles of competition. If this new pro- 

 cess should prove to be what it promises, a new and dangerous 

 rival to the silk-trade will have to be reckoned with. 



The composition of silk may be briefly described as follows : it 

 is a relatively strong, brilliant material, the produce of the digestive 

 juices of the worm acting on the leaves of the mulberry that con- 

 stitute its food. The cellulose of the leaf is triturated by the 

 worm, and transformed by its special organism into a peculiar 

 substance, transparent, and somewhat resembling horn. This is 

 called kerotine, and it fills two glands, from which it exudes in the 

 form of two threads, which unite as soon as they leave the body of 

 the worm. But this material no longer possesses the chemical 

 composition of cellulose : it is largely combined with a new ele- 

 ment characteristic of animal tissues, — nitrogen. The silk-fibre 

 thus discharged forms a continuous thread, which often reaches 

 the great length of 350 metres, the diameter of the fibre being only 

 eighteen thousandths of a millimetre. 



It was reserved for the present generation of inventors to devise 

 a means of imitating by science the mechanical and chemical func- 

 tions of the silkworm. 



An old student of the Ecole Polytechnique, M. le Comte de 

 Chardonnet, set himself some time ago to try and solve the prob- 

 lem. He took as his material pure cellulose, — a material, as we 

 have seen, entirely different to that of which natural silk is com- 

 posed. Cellulose is, as is well known, the basis of vegetable tis- 

 sues, and particularly of wood. Thus all soft woods appeared to 

 be well adapted for the purpose : in fact, any material saitable for 

 the production of a good quality of paper — white wood, cotton 

 waste,"etc. — appeared fitted for the production of artificial silk. 

 Paper pulp is, in fact, the starting-point of the industry. The first 

 operation to which the pulp is subjected is that of nitration, which 

 transforms it into pyroxile. This is done by steeping the pulp in a 

 perfectly defined mixture of sulphuric acid and nitric acid. After 

 thorough washing and drying, the nitrated cellulose is formed into 

 collodion by dissolving it in a mixture of 38 parts of ether and 42 

 parts of alcohol. The collodion thus made is drawn into fibre by 

 the mechanical means which will be described presently, but the 

 thread requires further and very important preparation. The fibre, 

 as it issues from the apparatus that imitates the glands of the silk- 

 worm, is one of the most inflammable of substances, and in that 

 state would be absolutely useless : an absolute process of denitra- 

 tion is therefore a necessity. Of this operation nothing can be 

 said, because it is kept a secret by the inventor. Its object is of 

 course to extract from the filament the greater part of the nitric acid 

 that it contains, and it would be curious to know if the nitrogen 

 that does remain after the process is in the same proportion as that 

 contained in natural silk. 



However this may be, the thread after treatment ceases to be 

 inflammable to any marked extent ; but it may, if desired, be ren- 

 dered still less liable to burn. After the denitration process, the 

 filament becomes gelatinous, and other substances can be incor- 

 porated with it. Thus, when in this state, it can be impregnated 

 with incombustible material, such as ammonia phosphate ; and it 

 is at this stage that the filament can be dyed to any desired color. 

 This latter operation cannot precede the denitration process, as 

 all the color would be taken out during that operation. 



The mode of manufacture is very simple, and in the exhibition 

 three apparatus are shown in operation to the public. The first of 

 these is only a model to illustrate the principle. The chief feature 

 consists of a glass tube reduced at the upper end to a capillary 

 passage. It is through this passage that the filament of collodion 

 is forced out under pressure. As it issues, the fibre is in a pasty 

 state, and would have no consistency if it did not consolidate im- 

 mediately. This solidification is secured by means of a second 

 glass tube, which surrounds the first one, and extends beyond it. 



