Fatôres que afetam a determinação da vitamina C na goiaba (Psidium guajava L.)

In the present paper the authors deal with the content of ascorbic acid in guavas (Psidium guajava L.) and the methods of sampling used. Ascorbic acid was determined directly in the photoeletric colorimeter (EEL), after extraction with a 4 per cent solution of oxalic acid. Guavas from various parts of State of S.Paulo were used and the general mean found was around 100 mgm of ascorbic acid per 100 gm fresh weight of the material used for extraction. It was found that there is great variation in the ascorbic acid content according to the condition of the fruit: Ascorbic acid Condition content in Mean mgm/100 gm Green and hard 93,36 - 119,54 102,43 Small green 57,34 - 92,30 83,40 Firm ripe 71,28 - 115,98 90,32 Overripe 63,22 - 85,98 77,36 Of the diferent parts of the fruit, the skin has the highest content; the pulp between the skin and the parts containing the seeds, the "inner pulp" contains little and finallw the central parts, formed by the pulp between seeds, the "inter pulp" a engligible amount. The proportion of ascorbic acid found in the skin, inner pulp and inter pulp may be as high as 1.6: 1: 0. Furthermore, the section near the peduncule and the sepals are richer than equatorial crossections. It was proved that the amount and intensity of sun-light is at least one important factant factor determining differences in the ascorbic acid content of the fruit, which is higer in the parts which have received more light. A sharp decrease was found in the vitamin C content of ripe fruite stored in a home refrigerator. The periods of the preservation were 12-24-48-96 hours and the decrease of the ascorbic acid content m per cent was 23.4 - 42.0 - 66.8 - 76.4 of the initial content of 144.28 mgm/100 gm. The following five different methods of sampling in the determination of the amount of vitamin C were tested, with extraction in a Waring blendor: 1) whole fruit; 2,) sample taken form fruits cut into many small pieces; 3) half of a fruit divided by a crossection at equal distance from both ends; 4) half of fruit divided lenghtwise; 5) a transversal slice of about 1 cm. It was found that the two first methods geve the most reliable results.

O brix na determinação da riqueza em açúcares do mamão como auxiliar no melhoramento do mamoeiro (Carica papaya L.)

There is in the literature a noteworthy lack of sampling methods to be employed in the selection of papaya fruits for genetical improvement purposes. In the present experiment methods applied to melon and watermelon were extended to papaya with good results. The authors tried to correlate the solids content-as determined by a hand refractometer-with total sugars in the fruit. The correlation does exist being significant and positive. A regression equation was worked out; it permits to calculate the total sugar content provided the Brix value determined by the hand refractometer is known. The equation is as follows: a = 0.57 s where a = total amount of sugar as glucose, and s = total solids.

Sorbímetro (Um aparêlho para a determinação das relações solo/água)

Os autores descrevem um aparelho destinado à medida contínua da água absorvida pela TFSA em condições de laboratório. O sorbímetro, cujo funcionamento obedece ao princípio dos vasos comunicantes, consta de um tubo em U cujos ramos verticais se ligam respectivamente à uma coluna de terra e à uma bureta de 100 ml. A bureta restabelece no tubo, a água absorvida pela terra. As leituras de bureta substituem as pesagens do método gravimétrico. O aparelho é recomendado para medidas a intervalos de tempo para os quais, o método usual é ineficiente.

Sôbre a determinação do nitrogênio, do fósforo e do potássio no mesmo extrato

The determination of total nitrogen, phosphorus, and potassium in plant material can be carried out in a common extract prepared with sulphuric acid and 30 per cent hydrogen peroxide. Nitrogen is estimated by direct nesslerization of a suitable aliquot (1-5 ml of the 50 ml extract made out of 250 mg of dried material); in order to avoid excessive acidity, 10 ml of Nessler's reagent should be employed. An aliquot of 1-5 ml suffices for the colorimetric determination of phosphorus by the molybdenum method; to reduce the phosphomolybdate complex 2 ml of a 2% SnC12 soln are necessary. Potassium is determined by the cobaltinitrite method after elimination of ammonium salts with the aid of aqua-regia.

Determinação da média aritmética e desvio padrão de quocientes de séries independentes e dependentes

The authors prove some approximate formulas for the computation of the mean and the standard error of quotients of two variates, correlated or uncorrelated, with not too high coefficient of variation. The formulas obtained are subsequently applied to some date on mensuration of horses of the Brazilian breed Mangalarga, by the eclectic system of LESBRE. The relsults obtained directly by the actual computation of the quotients as well as by means of the formulas with the aid of statistics of the numerators and the denominators are given in table 3, showing excellent agreement.

A absorção de nitrogênio, fósforo, potássio, cálcio, magnésio, enxôfre e silício pela cana de açúcar, Co 419, e o seu crescimento em função da idade

This paper describes the data obtained for the growth of sugar cane, Variety Co 419, and the amount and rate of absorption of nitrogen, phosphorus, potassium, calcium, magnesium, sulfur, and silicon, according to the age of the plant, in the soil and climate conditions of the state of S. Paulo, Brazil. An experiment was installed in the Estação Experimental de Cana de Açúcar "Dr. José Vizioli", at Piracicaba, state of S. Paulo, Brazil, and the soil "tèrra-roxa misturada" presented the following composition: Sand (more than 0,2 mm)........................................................................ 8.40 % Fine sand (from 0,2 to less than 0,02 mm)................................................. 24.90 % Silt (from 0,02 to less than 0,002 mm)...................................................... 16.40 % Clay (form 0,002 mm and less)................................................................ 50.20 % pH 10 g of soil and 25 ml of distilled water)..................................................... 5.20 %C (g of carbon per 100 g of soil)................................................................. 1.00 %N (g of nitrogen per 100 g of soil)............................................................... 0.15 P0(4)-³ (me. per 100 g of soil, soluble in 0,05 normal H2SO4) ............................... 0.06 K+ (exchangeable, me. per 100 g of soil)....... 0.18 Ca+² (exchangeable, me. per 100 g of soil)...... 2.00 Mg+² (exchangeable, me. per 100 g of soil)...... 0.66 The monthly rainfall and mean temperature from January 1956 to August 1957 are presented in Table 1, in Portuguese. The experiment consisted of 3 replications of the treatments: without fertilizer and with fertilizer (40 Kg of N, from ammonium sulfate; 100 Kg of P(2)0(5) from superphosphate and 40 Kg K2 O, from potassium chloride). Four complete stools (stalks and leaves) were harvested from each treatment, and the plants separated in stalks and leaves, weighed, dried and analysed every month from 6 up to 15 months of age. The data obtained for fresh and dry matter production are presented in table 2, and in figure land 2, in Portuguese. The curves for fresh and dry matter production showed that fertilized and no fertilized sugar cane with 6 months of age presents only 5% of its total weight at 15 months of age. The most intense period of growth in this experiment is located, between 8 and 12 months of age, that is between December 1956 and April 1957. The dry matter production of sugar cane with 8 and 12 months of age was, respectively, 12,5% and 87,5% of the total weight at 15 months of age. The growth of sugar cane in relation to its age follows a sigmoid curve, according to the figures 1, 2 and 3. The increase of dry matter production promoted by using fertilizer was 62,5% when sugar cane was 15 months of age. The concentration of the elements (tables 4 and 5 in Portuguese) present a general trend of decreasing as the cane grows older. In the stalks this is true for all elements studied in this experiment. But in the leaves, somme elements, like sulfur and silicon, appears to increase with the increasing of age. Others, like calcium and magnesium do not show large variations, and finally a third group, formed by nitrogen, phosphorus and potassium seems to decrease at the beginning and later presents a light increasing. The concentration of the elements was higher in the leaves than in the stalks from 6 up to 15 months of age. There were some exceptions. Potassium, magnesium and sulfur were higher in the stalks than in the leaves from 6 up to 8 or 9 months of age. After 9 months, the leaves presented more potassium, magnesium and sulfur than the stalks. The percentage of nitrogen in the leaves was lower in the plants that received fertilizer than in the plants without fertilizer with 6, 7, 8, 10, 11 and 13 months of age. This can be explained by "dilution effect". The uptake of elements by 4 stools (stalks and leaves) of sugar cane according to the plant age is showed in table 6, in Portuguese. The absorption of all studied elements, nitrogen, phosphorus, potassium, calcium, magnesium, sulfur and silicon, was higher in plants that received fertilizer. The trend of uptake of nitrogen and potassium is similar to the trend of production of dry matter, that is, the maximum absorption of those two nutrients occurs between 9 and 13 months of age. Finaly, the maxima amounts of elements absorbed by 4 stools (stalks and leaves) of sugar cane plants that received fertilizer are condensed in the following table: Element Maximum absorption in grams Age of the plants in months Nitrogen (N) 81.0 14 Phosphorus (P) 6.8 15 Potassium (K) 81.5 15 Calcium (Ca) 19.2 15 Magnesium (Mg) 13.9 13 Sulfur (S) 9.3 15 Silicon (Si) 61.8 15 It is very interesting to note the low absorption of phosphorus even with 100 kg of P2O5 per hectare, aplied as superphosphate. The uptake of phosphorus was lower than calcium, magnesium and sulfur. Also, it is noteworthy the large amount of silicon absorbed by sugar cane.

O método potenciométrico na determinação do H+ trocável em solos

For the determination of exchangeable hydrogen ion in soils, the authors of the presente work made the extraction with normal calcium acetate solution that may have an initial pH between 7 and 8 without altering the amount of hydrogen ion extracted. The extraction was made by shaking 5,0 grams of air dry soil with 100 ml of normal calcium acetate solution, the pH of wich was ascertained to 7,0, 7,5 and 8,0 with acetic acid, in 250 mil conical flasks for 30 minutes in a Wagner shaker (30-40 rpm). The contents of the flasks were then, filtered. A 50 ml aliquot of each of the leachate was titrated with a 0,020 N NaOH solution and the volumes consumed sodium hydroxide were ploted against pH. The titration curves thus obtained showed to be straight lines between pH 8 and 9 and parallel to the curve obtained by the titration of the blank. Two ways of locating the end point of the titration showed to be possible: the use of a pHmeter or titrimeter or the use of phenolphtalein as indicator. When using a pH meter or a titrimeter, the end point may rest in any point between pH 8 and 9, and the volume of sodium hydroxide consumed is found by comparison with a similar curve obtained by the titration of the blank. When using phenolphtalein the calcium acetate solution must have a pH below 8.

Determinação e comparação dos valôres Mi, A, Y e S, em dois tipos de solo do est. de S. Paulo

No presente trabalho, determinou-se e comparou-se os valores Mi de BARBIER et al., 1954, SCHEFFER e ULRICH, 1958, A de FRIED e DEAN, 1952 Y de LARSEN, 1952, e S de SOKOLOV, 1958, em dois tipos de solo do Estado de São Paulo: terra roxa legítima e um solo arenoso do campo da Secção Técnica de Química Agrícola da Escola Superior de Agricultura "Luiz de Queiroz". Aplicou-se 23,58 mg de fósforo, por vaso, na forma de superfosfato simples, contendo fósforo radioativo com uma atividade de 120.736 ipm; na forma de solução, aplicou-se também 200 mg de NH4N0(3) e 100 mg de KC1. Misturou-se bem para que houvesse homogenização a mais perfeita possível. Depois plantou-se 25 sementes de trigo, variedade 1146BH, deixando-se apenas 16 plantas após o desbaste. Procedeu-se àcolheita 55 dias após o plantio. Tanto a parte aérea como as raízes foram sêcas em estufa a 70-80°C. Sôbre o material triturado, digerido e diluído, retirou-se partes alíquotas para a determinação do P81 e do P32. Os valores obtidos para os dois tipos de solos foram os seguintes: mg de P por 1,5 kg de solo Valores Terra roxa legítima Solo arenoso Mi 177,96 92,62 A 177,55 92,71 Y 178,97 92,98 S 173,42 64,75 A análise estatística não revelou diferença significativa entre os valores Mi, A e Y, mas sim dêstes para o valor S. Quanto a este último valor, pode-se dizer que quanto mais rico em fósforo fôr o solo e quanto menor fôr o teor dêste elemento na semente, quanto mais êle deverá se aproximar dos valores Mi, A e Y.

Determinação polarografica do zinco em plantas, após a sua separação em resina trocadora de íons

O presente trabalho relata os dados obtidos na determinaçao do zinco em plantas segundo uma nova técnica. Esta nova técnica consistiu em se aliar a separação do zinco de outros interferentes, através do emprego de uma coluna de resina trocadora de anions, ao método polarografico da dosagem do citado elemento. A amostra de planta (1, 000g) foi incinerada em copo de Pyrex a 450-5009C durante 90 minutos e o zinco foi extraido da cinza com solução de HC1 2N. A separação do zinco de outros elementos interferentes foi feita pela passagem da solução através da resina trocadora de anions, Amberlite, IRA-401. Após a eluiçao do zinco da coluna, a solução obtida foi levada ao polarografo registrador. (Sargent, modelo XXI) para a determinação, Trabalhando-se com um conjunto de 10 (dez) a 12 (doze) colunas de resina, pode-se executar 10 (dez) a 12 (doze) determinações num periodo de 6 (seis) horas.

Determinação do zinco em vegetais pelo método do zincon

Este trabalho teve por objetivo o estudo do método de separação do zinco dos outros elementos por meio de resina trocadora de ânions (III, Merck), e a sua determinação colorimétrica por meio do Zincon, em vegetais. Estudou-se particularmente: 1 - estabilidade do complexo; 2 - formação do complexo em diversos pH; 3 - a influencia da concentração de ácido clorídrico na adsorção do zinco pela resina; 4 - efeito do volume de KC1 e NaNO3 na eluição do zinco ; 5 - influência de outros íons; 6 - exatidão e precisão do método; 7 - estudo comparativo de três métodos de preparo do extrato de vegetais.

Amostragem no mamão para a determinação do brix

The present paper deals with sampling methods to be employed in the determination of the total sugar content obtained from brix measurements in Carica papaya L., given by Zeiss hand refractometer. The results obtained led to the conclusion that, rather than using several samples per fruit, it is better to get a large number of fruits, taking just one sample per fruit. The sample in each fruit should be taken always from the same region.

Sôbre uma modificação na determinação do Molibdênio em Plantas

The author proposed a new modification on the thiocyanate-stannous chloride method for the determination of molibdenum, when is used a heavier-than-water solvent for extrating the colored molybdenum thiocyanate complex. Carbon tetrachloride - butyl alcohol is the mixture proposed, and the results obtained give a good precision and more sensibility than the other method that use carbon tetrachloride-isoamyl alcohol as extractant.

Determinação de cálcio "trocável" em solos por fotometria e chama

O presente trabalho relata o método de determinação do cálcio "trocável" dos solos do Estado de São Paulo, baseado na fotometria de chama. O método baseado na fotometria de chama foi comparado com o permanganométrico, através da determinação do cálcio "trocável" em 10 amostras de terra, tendo sido feitas 5 repetições com cada método. QUARDO 4 Cálcio «trocável» em solos, determinado pelo método permaíiganométrico e por fotometria de chama (média de 5 repetições). Solo Permanganometria Fotometria de chama n.o e. mg/100 g de solo e.mg/100 g de solo 1 3,58 ± 0,004 3,75 ± 0,040 2 2,60 ± 0,059 2,53 ± 0,026 3 0,54 ± 0,025 0,69 ± 0,034 4 0,39 ± 0,036 0,37 ± 0,020 5 3,61 ± 0,027 3,22 ± 0,044 6 9,41 ± 0,038 9,40 ± 0,074 7 1,00 ± 0,000 0,93 ± 0,001 8 1,79 ± 0,032 1,53 ± 0,069 9 1,00 ± 0,000 0,92 ± 0,000 10 0,60 ± 0,027 0,58 ± 0,033 Foi estudada também a influência de diversos íons (magnésio, manganês, potássio, sódio, ferro, alumínio e fosfato) na determinação do cálcio por fotometria de chama. O método de determinação do cálcio "trocável" do solo, baseado em fotometria de chama forneceu resultados equivalentes ao método permanganométrico, com enorme vantagem na rapidez.