Cotton Fibre Quality

The characteristics of cotton which are of the importance in the assessment of its quality include fineness,length,maturity,uniformity,and grade.All but the latter term have been considered already but the term 'grade' requires explanation.One of the main function of the men who handle the cotton between grower and spinner is to make available to the spinner a range of different types of cotton from which he may choose a type suitable for the purpose in view,e.g.hosiery yarn,fine yarn for shirting,etc.When the type of cotton has been decided upon,the spinner requires a certain degree of uniformity and continuity in the quality of the raw material delivered to his mill.Since cotton quality varies from year to year,field ti field,and bale to bale,some system of classification or grading must be used to ensure that the spinner receive his cotton in smoothly running lots,otherwise the problem continual readjustment and setting of the processing machinery will become great indeed.
When grading itself is considered we again meet variation,this time in the method used in grading and even difference in the terminology. Differences between centers separated by great distances can e understood to some extent,but we find that differences in grading cotton exist between markets relatively close together,e.g.Egypt and Sudan.It is not intended to discuss all the grading systems but to illustrate two which employ different criteria of evaluation.

American Cotton Grading:

The grading of American Upland cotton is based upon three main characteristics: color,trash content or foreign matter,and preparation.It is important to note that staple length is not one of the three.The color may be referred to as extra white,white,spotted,tinged,and yellow stained,in decreasing orderof merit.The variety,weather,soil,picking efficiency,and so on govern the color.

Foreign matter or trash consists of such materials as broken leaf and pod,sand and dirt.Some types are relatively easy to remove during processing.e.g.sand,but cute seeds with fibre still adhering to them are troublesome.Increased use of mechanical pickers leads to an increase in trash since the machine cannot exercise card or discriminate,as can a human cotton pickers.

The efficiency of ginning process is reflected in the assessment of the preparation.Poor ginning may result in damage fibre,neps,and stringy looking lint.Good preparation is denoted by an 'A' credit,poor preparation a 'C' with an intermediate category 'B'.
The United State Department of Agriculture has a series of standards for cotton grade.In 1941,thirty-two grades were officially recognized but these are based on eight on main grades:

Serial No	Cotton Grading
1 2 3 4 5 6 7 8	Middling fair Strict good middling Good middling Middling Strict low middling Low middling Strict good ordinary Good ordinary

It is interested to note that the grade 'Middling' is used as a basis for pricing of American cotton.
It is pointed out by lord that,even when suitable type standards have been inaugurated there are still serious problem.Type standards require continual replacement if their character is likely to change over a period of time.Moreover,interpretation of type standards in everyday practices by different people at different place also make calls personal skill.

Sudan-Egyptian Cotton Grading:

In the cotton growing region of the Gezira plain,the cotton is grade into six full grades.1 to 6 in descending order of quality,with half-grades denoted by 'X' a symbol foe 'Extra'.The classifier includes an assessment of the staple length in his judgment of the cotton,as well as

fineness,appearance,color,and trash content.The initial grading is made on the cotton before it is ginned and may be regraded at a second examination after it has reached the shipping point of port Sudan.The effect of the inclusion of a length assessment and the reduction of the importance of trash content as compared with American grading practice will be appreciated by a study of the graphs in figures.The reader is recommended to expand his knowledge of cottons and cotton quality by further study of the literature,in particular the papers by Lord on the production and characteristics of the world's cotton crops.

The Measurement of trash content

In the previous section,reference to trash content have been made.The machine used for its determination is an instrument developed by the British cotton Industry Research Association and made by Platts.The details of the analyzer are given belloand have been condensed from the makers describe booklet.

The machine operates on the principal of 'buoyancy separation' by the use of air current.The separation of cotton and the trash takes place as the two travel with the air stream through the settling chamber,the heavy trash particles falling almost straight down to the trash tray.On the other hand,as the single cotton hairs are entirely controlled by the air stream they are carried along with it and out of the chamber.The light trash particles tend to fall, but they are taken some way by the air stream.By correct adjustment of the air currents they ultimately fall into the trash tray at a point further forward than the heavier particles.The paths of the various particles are indicated by the dotted lines.