Principles and practice of agricultural analysis. Volume 3 (of 3), Agricultural products

by Harvey Washington Wiley

Manipulation.—Twenty-five cubic centimeters of each solution are mixed with fifty of water and boiled. To the boiling mixture twenty-five cubic centimeters of the levulose solution are added, which must not contain more than one per cent of the sugar. The boiling is then continued for fifteen minutes, and the cuprous oxid collected, washed and reduced to the metallic state in the usual way. The quantity of levulose is then determined by inspection from the table given below. Other methods of determining levulose in mixtures will be given further on.

Table for the Estimation of Levulose.

• (A) = Milligrams of copper.
• (B) = Milligrams of levulose.

(A)	(B)	(A)	(B)	(A)	(B)	(A)	(B)
20	7.15	62	31.66	104	56.85	146	82.81
21	7.78	63	32.25	105	57.46	147	83.43
22	8.41	64	32.84	106	58.07	148	84.06
23	9.04	65	33.43	107	58.68	149	84.68
24	9.67	66	34.02	108	59.30	150	85.31
25	10.30	67	34.62	109	59.91	151	85.93
26	10.81	68	35.21	110	60.52	152	86.55
27	11.33	69	35.81	111	61.13	153	87.16
28	11.84	70	36.40	112	61.74	154	87.88
29	12.36	71	37.00	113	62.36	155	88.40
30	12.87	72	37.59	114	62.97	156	89.05
31	13.46	73	38.19	115	63.58	157	89.69
32	14.05	74	38.78	116	64.21	158	90.34
33	14.64	75	39.38	117	64.84	159	90.98
34	15.23	76	39.98	118	65.46	160	91.63
35	15.82	77	40.58	119	66.09	161	92.26
36	16.40	78	41.17	120	66.72	162	92.90
37	16.99	79	41.77	121	67.32	163	93.53
38	17.57	80	42.37	122	67.92	164	94.17
39	18.16	81	42.97	123	68.53	165	94.80
40	18.74	82	43.57	124	69.13	166	95.44
41	19.32	83	44.16	125	69.73	167	96.08
42	19.91	84	44.76	126	70.35	168	96.77
43	20.49	85	45.36	127	70.96	169	97.33
44	21.08	86	45.96	128	71.58	170	97.99
45	21.66	87	46.57	129	72.19	171	98.63
46	22.25	88	47.17	130	72.81	172	99.27
47	22.83	89	47.78	131	73.43	173	99.90
48	23.42	90	48.38	132	74.05	174	100.54
49	24.00	91	48.98	133	74.67	175	101.18
50	24.59	92	49.58	134	75.29	176	101.82
51	25.18	93	50.18	135	75.91	177	102.46
52	25.76	94	50.78	136	76.53	178	103.11
53	26.35	95	51.38	137	77.15	179	103.75
54	26.93	96	51.98	138	77.77	180	104.39
55	27.52	97	52.58	139	78.39	181	105.04
56	28.11	98	53.19	140	79.01	182	105.68
57	28.70	99	53.79	141	79.64	183	106.33
58	29.30	100	54.39	142	80.28	184	106.97
59	29.89	101	55.00	143	80.91	185	107.62
60	30.48	102	55.62	144	81.55	186	108.27
61	31.07	103	56.23	145	82.18	187	108.92
(A)	(B)	(A)	(B)	(A)	(B)	(A)	(B)
188	109.56	232	138.57	276	168.68	320	199.97
189	110.21	233	139.25	277	169.37	321	200.71
190	110.86	234	139.18	278	170.06	322	201.44
191	111.50	235	140.59	279	170.75	323	202.18
192	112.14	236	141.27	280	171.44	324	202.91
193	112.78	237	141.94	281	172.14	325	203.65
194	113.42	238	142.62	282	172.85	326	204.39
195	114.06	239	143.29	283	173.55	327	205.13
196	114.72	240	143.97	284	174.26	328	205.88
197	115.38	241	144.65	285	174.96	329	206.62
198	116.04	242	145.32	286	175.67	330	207.36
199	116.70	243	146.00	287	176.39	331	208.10
200	117.36	244	146.67	288	177.10	332	208.83
201	118.02	245	147.35	289	177.82	333	209.57
202	118.68	246	148.03	290	178.53	334	210.30
203	119.33	247	148.71	291	179.24	335	211.04
204	119.99	248	149.40	292	179.95	336	211.78
205	120.65	249	150.08	293	180.65	337	212.52
206	121.30	250	150.76	294	181.63	338	213.25
207	121.96	251	151.44	295	182.07	339	213.99
208	122.61	252	152.12	296	182.78	340	214.73
209	123.27	253	152.81	297	183.49	341	215.48
210	123.92	254	153.49	298	184.21	342	216.23
211	124.58	255	154.17	299	184.92	343	216.97
212	125.24	256	154.91	300	185.63	344	217.72
213	125.90	257	155.65	301	186.35	345	218.47
214	126.56	258	156.40	302	187.06	346	219.21
215	127.22	259	157.14	303	187.78	347	219.97
216	127.85	260	157.88	304	188.49	348	220.71
217	128.48	261	158.49	305	189.21	349	221.46
218	129.10	262	159.09	306	189.93	350	222.21
219	129.73	263	159.70	307	190.65	351	222.96
220	130.36	264	160.30	308	191.37	352	223.72
221	131.07	265	160.91	309	192.09	353	224.47
222	131.77	266	161.63	310	192.81	354	225.23
223	132.48	267	162.35	311	193.53	355	225.98
224	133.18	268	163.07	312	194.25	356	226.74
225	133.89	269	163.79	313	194.97	357	227.49
226	134.56	270	164.51	314	195.69	358	228.25
227	135.23	271	165.21	315	196.41	359	229.00
228	135.89	272	165.90	316	197.12	360	229.76
229	136.89	273	166.60	317	197.83	361	230.52
230	137.23	274	167.29	318	198.55	362	231.28
231	137.90	275	167.99	319	199.26	363	232.05
(A)	(B)	(A)	(B)	(A)	(B)	(A)	(B)
364	232.81	370	237.39	376	241.87	382	246.25
365	233.57	371	238.16	377	242.51	383	247.17
366	234.33	372	238.93	378	243.15	384	248.08
367	235.10	373	239.69	379	243.79	385	248.99
368	235.86	374	240.46	380	244.43
369	236.63	375	241.23	381	245.34

147. Precipitation of Sugars with Phenylhydrazin.—The combination of phenylhydrazin with aldehyds and ketones was first studied by Fischer, and the near relationship of these bodies to sugar soon led to the investigation of the compounds formed thereby with this reagent.[112] Reducing sugars form with phenylhydrazin insoluble crystalline bodies, to which the name osazones has been given. The reaction which takes place is a double one and is represented by the following formulas:

• Dextrose. Phenylhydrazin. Dextrose-phenylhydrazone.
• C₆H₁₂O₆ + C₆H₅NH.NH₂ = C₆H₁₂O₅.N.NHC₆H₅ + H₂O
• and C₆H₁₂O₅.N.NHC₆H₅ + C₆H₅NH.NH₂ =
• Phenyldextrosazone.
• C₆H₁₀O₄(N.NHC₆H₅)₂ + 2H₂O.

The dextrosazone is commonly called glucosazone. The osazones formed with the commonly occurring reducing sugars are crystalline, stable, insoluble bodies which can be easily separated from any attending impurities and identified by their melting points. Glucosazone melts at 205°, lactosazone at 200° and maltosazone at 206°.

The osazones are precipitated in the following way: The reducing sugar, in about ten per cent solution, is treated with an excess of the acetate of phenylhydrazin in acetic acid and warmed to from 75° to 85°. In a short time the separation is complete and the yellow precipitate formed is washed, dried and weighed. The sugar can be recovered from the osazone by decomposing it with strong hydrochloric acid by means of which the phenylhydrazin is displaced and a body, osone, is formed, which by treatment with zinc dust and acetic acid, is reduced to the original sugar. The reactions which take place are represented by the following equations:[113]

• Glucososone.
• C₆H₁₀O₄(N.NH.C₆H₅)₂ + 2H₂O = C₆H₁₀O₆ + 2C₆H₅N₂H₂
• Dextrose (Glucose).
• C₆H₁₀O₆ + H₂ = C₆H₁₂O₆.

For the complete precipitation of dextrose as osazone Lintner and Kröber show that the solution of dextrose should not contain more than one gram in 100 cubic centimeters. Twenty cubic centimeters containing 0.2 gram dextrose should be used for the precipitation.[114] To this solution should be added one gram of phenylhydrazin and one gram of fifty per cent acetic acid. The solution is then to be warmed for about two hours and the precipitate washed with from sixty to eighty cubic centimeters of hot water and dried for three hours at 105°. One part of the osazone is equivalent to one part of dextrose when maltose and dextrin are absent. When these are present the proportion is one part of osazone to 1.04 of dextrose. Where levulose is precipitated instead of dextrose 1.43 parts of the osazone are equal to one part of the sugar.